Sprint 4G coverage for its 3G network is bigger & more reliable than AT&T. However, its 4G coverage is only available in select areas.
There are 3 kinds of mobile broadband. Postpaid, prepaid and rental. Postpaid offers discounted equipment in exchange for a long term contract. Prepaid offers no contracts in exchange for full price equipment. Rental offers no contract or equipment ownership in exchange for a higher overall cost.