Space Mountain ~ no matter where you sit, you are gonna get shook.
RNR ~ if you request front row or at least first few rows it is much smoother.
Guardians ~ SMOOTH but it is the nauseous factor here if you can do it.
TRON ~ SMOOTH but fast with banking, and very very short.
EE ~ it is a bit of everything, forward, backward, inside out, banking, drops ...
I hate Space Mountain anymore. After riding in DL there is no excuse for Disney World's to be so jerky and painful. I skip it 90% of the time. Hoping our new BTMR is as good as DL now. We do all the rest, and I have vertigo.
To OP ~ what gives you the headaches? Jerkiness, Upside Down, Backwards .. ? There are no smoother coasters at Disney than Guardians and TRON.