Its a pretty broad question
Personally I'd go with the 34, newer, more attractive etc etc.
Make sure you get one with low kays, and have a look around the exhaust to see if there is much oil on the bumper. Better still get the owner to rev it to 2000, then 3000, then 4000 only for a few seconds and see if there is any junk coming out.
Take it for a drive and listen for any unusual sounds or behavior
Theyre both good really I just prefer 34's to 33's