I have a few.
-Mean Streak at CP. Everybody said it was a horrible ride and was excessively painful. I found the ride to be fun and fairly smooth. Sure, it wasn't GCI smooth, but wasn't bad at all.
-Mantis at CP. Again, everybody said that the ride sucked in every seat. It was a smooth ride with small pumps here and there. I thought it was just as good as Riddler's Revenge.
-Millennium Force at CP. Lots of people said that the hills didn't have any airtime. I was surprised when I rode it for the first time. I tried the front, middle, and back, and the middle had the best airtime. The last hill (the one parallel to the station) had ejector in the middle seat. Maybe I just got a good day.
-X2 at SFMM. I rode the coaster once over 2 1/2 years ago. I hated it. I rode it once and only once. I when back to SFMM yesterday and gave it another shot and I was amazed. The ride was fantastic! It easily went from my least favorite ride to my top 5!
-Last one. Viper at SFMM. Like X2, it's been a while since I have ridden Viper. I gave it a shot in the front seat and it was awesome (as awesome as an Arrow can get). The loops were fun and the ride was fairly smooth; and being a 5'2" kid, with the restraint as tight as it will go and still being loose, I had lots of freedom from head-banging. I even had ejector airtime (yes, ejector) on the transition from the upward climb to the brake run. It was a lot of fun!
EDIT: I would also like to add TTD as an unpleasant surprise. I was THRILLED for this coaster from all the hype it gets (and how much better it is than KK). I rode it in the middle row and was very disappointed. It was over too soon to thoroughly enjoy the ride. Not to mention, I was disappointed with the launch. Xcelerator's is WAY more intense. Still a great ride, but I'll take Maverick or Xcelerator over it any day.