Wired.com has a nice article that explains what is 4G data service and how the U.S. mobile carriers are providing 4G data service. You may know that there has been a considerable amount of sarcasm on the Internet about the carrier’s claims about their 4G networks because by the full definition of the standard none of the networks meet the standard.
According to the International Telecommunication Union (ITU) standards, 4G networks have download speeds betwen 100 Mbps and 1 Gbps, and none of the U.S. networks come close to that mark. In December the ITU began allowing the use of the “4G” label for forerunners of true 4G networks as well as evolving 3G networks, therefore opening the door for all of the providers to claim they provide a 4G network.
In the simplest terms, a provider’s 4G network is newer and faster than the current network that you are most likely using. If you are the type of person who has to use the fastest network my recommendation is to ignore whatever label the provider uses for their network and ask what are the practical download and upload speeds. Be aware that most providers will quote the theoretical peak speeds of their networks, and no network, not even wired networks, meet the theoretical peaks because speeds slow down as more people use the network.
The Wired.com article does a good job of providing the technologies, claimed (practical) speeds and theoretical max speeds, along with cost and availability. My recommendation is to focus first and foremost on availability in the areas where you will connect to the network. Next, if you can shop around, seek out people who already use the networks where you plan to use it and ask them what speeds they see. Bandwidth speed test apps are available for every smartphone platform.