3G iPhone with O2 or Orange?

I get one, no contract, just go, this network is the best? Orange may have better coverage, but it is very poor where I am right now. O2 doesn't have a fair usage policy as Orange for iPhone 3G user then maybe they will not be as stringent. What is 1 of 2 have a better distribution plans? What should I choose? Please help

o2 have excellent reception where I go and I think they are the best, but orange is always a good network