This is merely a edited version of a post I made on WebHostingTalk.com (WHT) some time ago (just over a year ago, actually), but many of the points are still relevant.
This isn't a definitive guide, as much as my personal method, little else.
Nowdays, I usually have virtual/reseller hosting with around six different webhosts at anyone time, just for my personal sites.
I simply hope it's generally helpful.
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When I'm looking for a web host I do a check on WHT for the host name. The first thing to look for is threads about re-occuring problems. Every business has major challenges. But no worthwhile business should face the same challenges repeatedly. If they do, ignore them.
Too few threads can also be a bad sign - or, more precisely, they're untested. While it would be unfair to new hosts to claim that implies anything regarding their service, the more recommendations a host has the better. Oh - and NOTE - ignore recommendations from WHT members with less than 100 posts. I've always suspected some hosts of creating sleeping aliases, to pop out only to recommend themselves.
Do also note that WHT is not the God of Webhosting - it is a collection of opinions and experiences. These do not define reality, but are a selective perception of it. So be prepared to take comments with a pinch of salt.
Also - if the host is present at WHT, observe how they deal with issues - most specifically, see how they deal with stress. If they are reported for bad service, do they reply in a mature manner, admit fault where required and apologise if so? This is a good sign of someone capable of running a business. Tantrums and abuse from a host suggest a lack of long-term thinking essential for business.
ALSO - keep an eye out for hosts that sound like they know what they're talking about. It doesn't mean to say that hosting is about single black-and-white-issues - but note to see if your potential future hosts at least shows an awareness of such topics where they have actually made replies on it. Anyone can start up a hosting business, but you want probably want to be with someone who can actually sustain your site environment and a business.
And there's more...
There's nothing wrong with statements such as "unlimited subdomains" or "unlimited databases", because the host is actually just telling you to use as much as your hosting package allows. A plan with 10 megabytes of diskspace won't leave much room for unlimited of much.
Unlimited space and bandwidth are definite indicators of trouble - namely, hidden charges, poor planning, uncertain resources.
Note also that when narrowing down hosts, see who they cater for. Some hosts have little time for newbies, so include a stupid question in your pre-sales e-mail. Often hosts make a trade-off of support vs resources. Those with best support will tend to charge more.
NEVER get carried away with impressive specifications if they are far beyond what you actually need. For example, why spend $20 on a plan offering 1 gig diskspace and 10 gig b/w when you actually only need the $10 plan of 50 megs diskspace and 2 gig b/w? Just because you
can have a thing doesn't mean you necessarily need it.
Consider time to reply to pre-sales e-mail as indicative of support. Only a rule of thumb, but it shows that the host/ support is online. Those who take a long time to answer are perhaps not online as often as they should. Those who cannot organise their e-mails enough to reply probably cannot organise a server either.
NEVER make a rushed decision. When you're narrowing your list, keep an eye on the companies. Not long ago I whittled down a list to 2 companies - then one suffered repeated crashes. So I snubbed them. Those crashes continued for months.
ALSO note that any list you make is not an objective list of the "best hosting companies". There is no list. You are making a targeted list according to your own specifications. For example, I made a list in December based on price. This week I made a list based on long-standing good-reputation, and then juggled my figures to see which would fit together within the final price range.
At the end of the day, when you're looking for a web host, you're looking for a host according to your own specific needs. Probably there are a number of hosts who can offer you good service. Apply some common sense, and a little time into researching said hosts. After all, if what you are looking for a is a long-term hosting commitment, you need to be able to at least spend a little effort and thought ensuring that what's right for you is really what you're looking at.