I used to hate roller coasters. My biggest problem with them was (and is) big drops where you pop out of your seat. This is known as "air time" and most coaster enthusiasts want it. I don't.
I tried Big Thunder Mountain Railroad first, among the WDW coasters. I loved it! If you push the bar down on your legs hard before you get going you won't pop out of your seat. There are no big drops but there are some little ones that would pop you up if you weren't squished in tightly. Then possibly try Space Mountain. Space Mountain is bumpier and jerks you around more. Sit toward the front for a smoother ride. There are still no big drops and the restraint system keeps you from popping up if you get it set really snug.
If you are comfortable with those, then try Rock N Roller Coaster or Expedition Everest. RnRC has loops, but you're in the dark and distracted by the music. Its fairly smooth (the smoothness has decreased over the years) and its over really fast. Everest is HIGH. I think the biggest drop is done backwards in the dark....no popping out of the seat. There is another big drop, but its curved and you're back up before you even know it. I almost didn't do this one when my dh was acting all impressed about how high and fast it was.....but I'm glad I did it. Its a great ride.
None of Disney's coasters are considered great by those who love the biggest, tallest, fastest, etc..... but they're great for coaster poultry. The only one that really has big hills is Everest, and even those aren't in the same sense as most amusement park coasters.
There are only a couple other fun fast rides.....Mission:Space at Epcot, Test Track at Epcot, Dinosaur at AK. Everything else is relatively slow moving. But they're more about the experience than the motion of the ride.
