Here's my top 3 for now:
1. Scream-n-Eagle at Oaks Park, which is a KMG Afterburner. It's just plain exciting!
2. Rock-o-Planes (I've only ridden the one at Oaks Park). They're fun because you control the experience, and they're even moderately scary, although I wouldn't call them "thrilling". I found myself saying bad words out of surprise the first time I rode one, which is not typical of me.
3. Gravitrons! (I've been on the Starship 2000 at a Funtastic carnival.) They're not in the least bit scary, but it's a fun sensation and concept. It's trippy to look sideways and down, and it's fun to try to "unglue" your head. They're also extremely creepy--imagine being alone in a dark, enclosed ride with just the operator! I've yet to try positioning myself upside down, etc. (if it's even allowed), which is apparently doable and common but looks unsafe to me. Anyway, they're decidedly more fun than Round-Ups, which I like but don't find very exciting.