whats the difference between the regular chevy cobalt, cobalt ss, and pontiac g5?

[Mocha:]] is back.]

im looking for a good first car for a teen. not exactly brand new but at least a 2004--present model and i originally wanted a Pontiac g5 but what exactly are the difference between these cars and which one should i get?
it has to be automatic
why or why not should i get each car?
thanks