On Wind, you have unlimited US roaming for $15 a month
Tmobile is cheapest at $2a day ($3 for 200MB per day of 4G speed) + $10 SIM. You eed to purchase prepaid credit in $10 blocks though.
http://prepaid-phones.t-mobile.com/p...ll-phone-plans
Roam mobility is $20 SIM card, that you need to wait for delivery or pick up before you go. This can be good if you want coverage during a layover etc. $4 a day for unlimited talk/text and 300MB 4G data , but you have to buy it in bundles of 1,3,7, 14 or 30 days
Roam Mobility resells T-Mobile service, so they are otherwise equiv in terms of coverage/speed/etc.