I love both, and was looking for a 97/98 Series 3 R33 when i stumbled across the 32 N1. Being an N1 it was a no brainer and i went with the 32.
Personally, I think the 33's look "classier" and a nice late model one with minimal mods looks stunning.
If your going to mod/rebuild engines, or buy one rebuilt then it should come down to simply what shape you like better. If you're going to keep it close to stock, a late model 33 can be almost 10 years newer than an early 32, so i would go the 33.
To sum up, I am of no help as i would take either one :-)