No experience personally with either of those two, but if you are not a heavy user and not need a 'family' plan I suggest you check into pre-paid plans. I use my phone rather infreq. and text one or two times a month. My annual bill is about $100 total.
Coverage on many is the same as AT&T or Verizon as several of them just buy access to these networks. Virgin and Boost use the Sprint network.
Check the coverage maps too, and ask a friend local to you how they think the service is too before making the jump. Check out a new one, Ting, as they let you select each option for voice/text/web seperately and basically fine-tune your plan to suit your usage. I've been considering AirVoice too, they have some ultra low rate plans, and get pretty great reviews. YMMV.
This wiki below is a great resource on comparing the various pre-paid plans for voice/text/web options: