It depends on the length of the flight.

For short flights (< 2 hrs), I don't care anything about in-flight service. It's whoever has the lowest airfare.

For longer flights, assuming all airlines have the same airfare, I am interested in the following (in order of importance):

4) Seat comfort
3) Entertainment (movie, tv, power outlets for laptops, etc.)
2) Food options
1) Ability to select my seat online at time of booking