I watched the original cartoon series, and then the live-action series a bit too. Michelangelo was my favorite as a kid, but now I'd probably pick Raphael or Leonardo. I never cared for Donatello much but he's alright too. The only thing I remember about Venus, the girl turtle from the live-action series, is that she was female. She was alright but seems to have been an unpopular character for some reason.
Shredder was my favorite villain, I guess. He was pretty cool in the movies.
My favorite memory is a pretty simple one. I had a bike horn as a little kid, and it was just pretty cool to me even though I didn't know how to ride a bike yet. It was like this one except it was Michelangelo instead: