I would normally look for in below order:
Support (Technical support is very important), Value for Price (you will get what you pay for), Uptime, Reliability!
. In the 8 months I've used Cloudarion.com
VPS hosting, I can only remember 1 significant session of downtime, and that was partially my own fault because I didn't update to a new server when they asked me to. They solved all the troubles. I am happy with them.