Looking to get a SIM for some Data and few minutes for a trip in the US, any advices ?

Hi, I'm leaving soon for a 3 weeks trip in the US and I'm looking to get a SIM card for my European Nexus 5 in order to make a few local calls (30mins to 1h) if needed and to get data for apps, mail and Maps (maybe 1Go, with the possibility to add some if needed).

So I'm looking for advices, a bit like empty86 gave after his trip in Europe.

I understand that Verizon and Sprint are out with their CDMA networks, so it leaves me with AT&T and T-Mobile. From the outside of the US and reading tech sites, T-Mobile seems more attractive than AT&T but I'm not staying only in cities (NY, Chicago) but also going to places where the networks may not be that great (Yellowstone NP and some canyons in Utah and Arizona). Will the T-Mobile network be good enough or should I stick with AT&T ?

After the Network problem, I still have to choose a Carrier. Is there interesting MVNO offers I can pick ou should I stick with the big names ? What kind of offer should I look for and in what kind of places ? I'll first stay in lower Manhattan, so I think I could find anything if I know where to look. :-)

Any advices would be greatly appreciated since the US phone services market looks quite complicated from France (and obviously super expensive).