A few of my friends have Nextel. After seeing how much they pay and the inferior coverage they have I see the walkie-talkie novelty as just that. Now that they are merged with sprint their coverage should get better as everything is slowly transitioned over to Sprint's network.
I have Verizon and while they are certainly the 800lb gorilla in the cell phone market I have excellent service damn near every place I have been in the US. They do have the best coverage and have finished 1st in Consumer Reports cell phone survey the past few years. While there is obviously no gurantee they would give you the best service, the probability is likely there.
HTH!
