Best Phone/Data option for someone spending 2 weeks in the US

Hello there Vergers,

I am from Brazil, and am planning on spending a couple of weeks in 'Merica in the following months, probably going through Washington, New York and Chicago.

Doing my time there I will probably get the new [REDACTED] phone because really, who doesn't get this phone sucks at life, and I would like to have an american SIM there in order to stay connected with the people back home, and friends in the US.

So, what would suggest as the best option for a non-american?

A pre-paid sim? Can those come with a lot of data, and if so, which carriers should I choose for these cities?

I also have the new iPad, which supports AT&T LTE, so I could just get a data only SIM and switch it between iPad and phone.

What do you American Vergers suggest?

Also, feel free to drop any geeky places you think are interesting in these cities, really, the geekier the better.