Airsoft is the name for a class of airguns that are designed to shoot plastic balls called BBs. They are generally less powerful than BB guns and pellet guns. The game played with those guns is also...
It all depends of the company making it. A Tokyo Marui M1A1 Thompson would be better than a cheap Wal-Mart M4. But a Classic Army M4 would be better than a CYMA M1A1 Thompson.
If you are just starting airsoft i would highly recommend an aeg, (airsoft electric gun) but if you are pro and experienced, a trained camouflaged sniper is the best, an invisible predator. However...