I'd say try out the Evo on Sprint, that way you can get a feel for their service, and Android in general. With their 30 day money back guarantee, it seems like the best way to test the waters on both fronts. If it works out, you would probably be able to then bring over your wife, and convert the plan to a family plan.

The only downside I can see with this route is the extra $10 a month Sprint likes to tack on to the Evo for 4G, even if you don't plan on using 4G.