It's simple, really. When you're with AT&T you're dependent upon their network. Same with Verizon, T-Mobile, Sprint and the rest.
NET10 is different. There's no "NET10 Network." NET10 uses AT&T, Verizon, T-Mobile and other carriers' networks.
The NET10 phones for sale in retail stores and online are configured to operate on the best possible network in each area they're sold. That's why some phones are available in certain areas and not others.
Roaming? There's never an extra charge for roaming with Net10 since you're never "out of network." In the rare instance you're in an area outside your primary network, NET10 has agreements with local networks for coverage. That's why you rarely hear about "dropped calls" or "dead zones" with NET10.
Better than any single network; that's NET10!