My main criteria is support and customer service. I find a host that has the specs I need then I contact them and ask some presales questions and base my decision on quickness of reply and quality of their reply.
I mainly base my decisions on support & customer service as well. I also look on price, not for cheap or expensive but "Just Right". Going too cheap can sometimes lead to disaster and going too expensive is just silly haha.
I'd pretty much do the same as @energizedit, by contacting the company with some pre-sales questions and looking for responsiveness and quality of responses.
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Support all the way. Considering that I am usually doing my site editing at off hours, it is imperative that the 24/7 chat is available. For some reason, I have a lot more patience waiting for a chat than waiting on the phone. That is my number one criteria when choosing a web host. Others would be price, reliability, and customer reviews.