For the mobile-broadband part, the 2 largest nation-wide carriers are AT&T (GSM/UMTS) and Verizon (CDMA). Their coverage should be more-or-less equal. If you are coming from Norway, then you should be familiar with GSM/UMTS since that's the 2G/3G technology used in Europe, so you may want to get an unlocked data card, so you could use it back home in Norway as well. Just be aware, in Europe GSM is on frequencies 900 and 1800 and UMTS on 2100, while in the USA GSM and UMTS are both on 850/1900. So check the frequencies before buying any data cards. Most newer cards support all freqs, for example:
Newegg.com - AT&T Sierra AC885 USB Unlock 3G Data Card - Cell Phone Accessories





