Low back? Neck/back?
I've got neck/upper back issues. (compressed discs, etc.)
I have problems with:
Space Mountain,(really wrenches my neck, I've stopped riding)
Dinosaur (especially lately, seems rougher).
I haven't ridden anything in galaxy's edge yet.
I have absolutely no issues with tot or rock and roller coaster, or everest, but this might be different with low back issues.
Safari depends on who is driving, or if it's rained recently. Sometimes it has a lot more gutting, and some drivers seem like they need to whip around, some seem to drive more reasonably.
No issues with slinky or mine train, both newer and smoother.
aliens is smooth and fine, ime, teacups- depends on who is doing the spinning.
Believe it or not, Pirates messed me up badly last few trips. (I've also had a similar problem on Mexico boat ride and The Land occasionally) They are stacking the boats up so much, that they tend to bash into each other at the end, and the constant slamming from behind did a number on my neck and back.