In terms of coaster roughness
Runaway Mine Train- It's a powered coaster so it's not very rough
Nemesis- For a 20 year old ride it's beautifully smooth, it may not be 100% but the last few rides I've had have been smooth as silk
Oblivion- very smooth
Air- it's smooth
Spinball- varies by ride, some train are rougher than others but shouldn't be anything too painful
Rita- probably the roughest coaster at the park. The ride does bash you about a fair amount.
Thirteen- nothing rough on this coaster
Smiler- first half of the ride isn't too bad, bad it does gets pretty rough on the second half especially on the last 3 inversions. If you're on trains 3 or 5 you should get a decent ride but on train 4 be prepared for rattly jolty ride.
That's my opinions on roughness but rides vary on different days and times.