-200 carries less passengers.
-200 engines have a smaller diameter than the -400.
-200 is definately older than the -400 and makes a lot more noise.
-400 devided by 200 equals 2 which is the number of required pilots on the flightdeck.
-200 got 2 overwing exits whereas the -400 has 4
Everything else is pretty much equal.
Do some more banner-towing i.s.o. applying for a crappy outfit like Ryanair.