Not only should the web host be reliable and fast, it should guarantee its uptime (the time when it is functional). Look for a minimum uptime of 99%. In fact, even 99% is actually too low it really should be 99.5% or higher. The host should provide some sort of refund (eg prorated refund or discount) if it falls below that figure. Note though that guarantees are often hard to enforce from your end especially if the host denies there was any downtime. However, without that guarantee, the web host will have little incentive to ensure that its servers are running all the time.
2. Data Transfer (Traffic/Bandwidth)
Data transfer (sometimes loosely referred to as "traffic" or "bandwidth") is the amount of bytes transferred from your site to visitors when they browse your site.
Don't believe any commercial web host that advertises "unlimited bandwidth". The host has to pay for the bandwidth, and if you consume a lot of it, they will not silently bear your costs. Many high bandwidth websites have found this out the hard way when they suddenly receive an exorbitant bill for having "exceeded" the "unlimited bandwidth". Always look for details on how much traffic the package allows. I personally always stay clear of any host that advertises "unlimited transfer", even if the exact amount is specified somewhere else (sometimes buried in their policy statements). Usually you will find that they redefine "unlimited" to be limited in some way.
In addition, while bandwidth provided is something you should always check, do not be unduly swayed by promises of incredibly huge amounts of bandwidth. Chances are that your website will never be able to use that amount because it will hit other limits, namely resource limits. For more details, see the article The Fine Print in Web Hosting: Resource Usage Limits.
To give you a rough idea of the typical traffic requirements of a website, most new sites that don't provide video or music on their site use less than 3 GB of bandwidth per month. Your traffic requirements will grow over time, as your site becomes more well-known, so you will need to also check their policy when you exceed your data transfer limit: is there a published charge per GB over the allowed bandwidth? Is the charge made according to actual usage or are you expected to pre-pay for a potential overage? It is better not to go for hosts that expect you to prepay for overages, since it is very hard to forsee when your site will exceed its bandwidth and by how much.
3. Disk space
For the same reason as bandwidth, watch out also for those "unlimited disk space" schemes. Many new sites (that don't host videos or music) need less than 20 MB of web space, so even if you are provided with a host that tempts you with 100 GB (or "unlimited space"), be aware that you are unlikely to use that space, so don't let the 100 GB space be too big a factor in your consideration when comparing with other web hosts. The hosting company is also aware of that, which is why they feel free to offer you that as a means of enticing you to host there. As a rough gauge, thesitewizard.com, with nearly 400 pages in April 2013, used only about 18 MB for all its pages and associated files.
4. Technical support
Does its technical support function 24 hours a day, 7 days a week (often abbreviated 24/7), all year around? Note that I will not accept a host which does not have staff working on weekends or public holidays. You will be surprised at how often things go wrong at the most inconvenient of times. Incidentally, just because a host advertises that it has 24/7 support does not necessarily mean that it really has that kind of support. Test them out by emailing at midnight and on Saturday nights, Sunday mornings, etc. Check out how long they take to respond. Besides speed of responses, check to see if they are technically competent. You wouldn't want to sign up with a host that is run by a bunch of salesmen who only know how to sell and not fix problems.
5. FTP, PHP, Perl, SSI, .htaccess, SSH, MySQL, Cron
If you are paying for a web hosting account, you really should make sure you have all of these.
Note that some commercial hosts do not allow you to install PHP or Perl scripts ("What is PHP and Perl?") without their approval. This is not desirable since it means that you have to wait for them before you can implement a feature on your site. The ability to create or modify ".htaccess" files is needed if you are to do things like customize your error pages (pages that display when, say, a user requests for a non-existent page on your site) or to protect your site in various ways (such as to prevent bandwidth theft and hotlinking, password-protect a directory (folder), etc).
SSH access is useful for certain things, including testing certain scripts (programs), maintaining databases, etc. MySQL ("What is MySQL?") is needed if you want to run a blog or a content management system. Cron is a type of program scheduler that lets you run programs at certain times of the day (eg, once a day). Check to see if these facilities are provided.
6. SSL (secure server)
If you are planning on selling any goods or services through your website, you may want to see if the web host lets you set up SSL (a secure server). You may have seen this on other websites where their web address begins with a "https://" instead of "http://". Setting this up will normally involve additional charges or a higher priced package. At this point, the main thing is do is to check if they are available at all before you commit to the host. You will definitely need to have SSL if you plan to collect credit card payments yourself. If you're relying on a payment gateway instead, and are not otherwise collecting sensitive or private information from your customers, it's possible that you don't need this facility. For those who are wondering about what this is, but are too lazy to click through the link in the previous sentence, a payment gateway is just a third party company, like PayPal, that collects credit card payments on your behalf.
7. Email, Autoresponders, POP3, Mail Forwarding
If you have your own site, you will probably want to have email addresses at your own domain, like sales@yourdomain.com, etc. Does the host allow you to set up whatever email addresses you want on your domain, so that mail can be forwarded to your current email address, or placed into a mail box on your web hosting account itself? Can you set an email address to automatically reply to the sender with a preset message (called an autoresponder)? Can you retrieve your mail with your email software?
8. Control Panel
This is called various names by different hosts, but essentially, they all allow you to manage different aspects of your web account yourself. Typically, and at the very minimum, it should allow you to do things like add, delete, and manage your email addresses, and change passwords for your account. I will not sign up with a host where I have to go through their technical support each time I want to change a password or add/delete an email account. Such tasks are common maintenance chores that every webmaster performs time and time again, and it would be a great hassle if you had to wait for their technical support to make the changes for you.
9. Multiple Domain Hosting and Subdomains
For those who are thinking of selling web space or having multiple domains or subdomains hosted in your account, you should look to see if they provide this, and the amount that they charge for it (and whether it is a one-time or monthly charge, etc).
10. Web Server and Operating System
Is the type of operating system and server important? I have discussed this issue at length in the article "Should You Choose a Linux or a Windows Web Hosting Package? Is There Such a Thing as a Mac Web Host?"
In general, most people will want to sign up for a web host offering a Unix-based system (like Linux, FreeBSD or OpenBSD) and running the Apache web server. Most web-based software assume your website is running on such a system, and you will usually experience fewer compatibility issues with it. There are also a lot of guides available on the Internet on configuring such systems, so finding help when you need it is easier as well.
In my opinion, the only time when you will want to use a Windows server is if you're running Windows-specific programs, like ASP scripts. But even then, you'll probably be better off looking for a PHP-equivalent, and using a Unix-based system.
11. Price
I was actually hesitant to list this, but I guess it's futile not to. However, I would caution that while price is always a factor, you should realise ("realize" in US English) that you often get what you pay for, although it's not necessarily true that the most expensive hosts are the best.
12. Monthly/Quarterly/Annual Payment Plans
Most web hosts allow you to select an annual payment plan that gives you a cheaper rate than if you were to pay monthly. My current personal preference is to pay monthly with all new web hosts until I'm assured of their reliability and honesty. Paying monthly allows me to switch web hosts quickly when I find that the current host does not meet my requirements: this way, I'm not tied down to a bad web host because I have prepaid for an entire year. I do this even if the new web host guarantees that they will refund the balance if I'm dissatisfied, since at the point I sign up, I have no assurance that they will honour their guarantee. Later (usually after a couple of years), when I'm satisfied with the host, I may change payment plans to the discounted annual plans.
13. Resellers?
Not all hosting companies own or lease their own web servers. Some of them are actually resellers for some other hosting company. The disadvantage of using a reseller is the possibility that you are dealing with people who don't know much about the system they are selling and who take longer to help you (they have to transmit your technical support request to the actual hosting company for it to be acted upon). However, this also depends on both the reseller and the underlying hosting company. It is thus wise not to rule out all resellers; there are a number of reliable and fast ones who are actually quite good and cheap. In fact, a number of resellers sell the same packages cheaper than their original hosting company. If you find out that a particular company is a reseller, you will need to investigate both the reseller and the real hosting company.
14. International
If you don't stay in the USA, you have the option of hosting your site with some local provider. The advantage here is the ease of dealing with them (they are after all easily accessible by phone call or a visit), your familiarity with the local laws and easy recourse to those laws should it be necessary. It should be your choice if your target audience is local (eg a local fast food delivery service). On the other hand, hosting it in USA has the advantage of faster access for what is probably the largest number of your overseas visitors (particularly if you have an English-speaking audience). You also have a large number of hosting companies to choose from, and as a result, cheaper prices too.
