I haven't seen "Watership Down" so I'm not gonna vote.
I'm pretty much in this situation as well. Although I've read the book, and I enjoyed it.
Watership Down is going to win, not only because it has cute fluffy animals, but because...it has cute fluffy animals.
Watership Down
It is awesome period.
Sure some parts scared the shit out of me,
since I was very young when I watched it,
but it was a movie, I never will forget.
I seriously need to watch it again - I haven't seen it since well before you were born. I remember a rabbit den/community, and then later a bunch of rabbits brutally attacking one of their own for reasons which I don't recall. *adds to list of many things to watch again*