Reliability is my number one highest priority. I don't want to get calls from customers saying their web site hosting is down or crawling along (then subsequently loosing them as a customer) and from a personal point of view I want my hobby sites to be working well at all times so I don't lose members.
Second is support. Should there be a problem I want it sorted ASAP. I don't want to submit an email, hope they've got it, wait a few hours for a reply (if any). I like to be able to get onto live chat and action be taken.
Third is speed. I hate
website hostings that crawl along and vary madly in speed.
Four is value for money. I like a good quality service for my money. I've tried more expensive hosts and I've been with cheaper ones. The price alone isn't the major factor but I do expect the hosting company to provide the service they advertise.
Overall, reliability of the hosting and support are my main two priorities.