whats the difference between these two which one is better?

Sentra is a 4 door, 200sx is a 2 door. The 200sx offered an SE-R model which had an sr20de motor and rear disc brakes. That's the one you should get.

i used to have a 96 200sx se-r and they're definitely awesome cars. i have never heard an NA 4 cylinder that sounded so damn good with an intake until the s2000 came out. and they're quick as hell with lots of available mods. I don't know how the hell they got the new se-R's from the old 200sx's and sentra's though.