I like the tactical feel of inserting a cartridge. (*insert dirty minded joke here*) But I can't say I like discs much either, as discs tend to wear down, or have bad scratches. I've brasso'ed/buffed out scratches in too many cd's/dvds to count, but I think cartridges are a little more classic.
However, I love my flashcart - I don't have to bring too many cartridges with me, and I don't have to worry about the contacts getting screwed up. (I knew one used game store guy who used very fine grit sandpaper to bring cartridges back to life.)