When selecting a wireless company, its really important to decide first on the quality of the service where you will be using the phone. If the signal is weak, or you have no service, you should consider other options.
After that, price and services would be the next thing to think about. Since most of the services only vary a little, price would be the big factor here.
You should never decide your carrier based on the phone first. But assuming you have taken into account the two things before this, it really just becomes a matter of opinion.
Ive been with Sprint for what seems like forever. Ive never really had an issue with them. I have, in the not too distant past, considered leaving them for an iPhone. I didnt. The Hero might truly be their hero in this case.
The most vocal customers are usually the unhappy ones. I can show you loads of people unhappy with AT&T (using just iPhone owners alone), VZ and they way they cripple their handsets, Sprint and T-Mo.
The other thing to consider is that your unlocked phone, may or may not have the right 3G radio in it, no 3G leaves you on the slower Edge.