Def the back for me. The front provides a great view, but not the same level of thrill. I love being whipped over hills.
However, I voted for front row, although there is some merit to the back row, especially for wooden coasters with twisting layouts, and older coasters with big drops. But for most modern hypers and inverted coasters the experience is almost always diminished unless you are in the front row.
Rarely do I sit anywhere but the front or back.
The Beast is bumpy as heck in the back which is a fun ride!
On visually intense steel rides- like Dueling Dragons and Millenium Force- I'll usually try for the front, at least for one ride.
Front Row FTW!
It's my first time doing it, though.
Front, Back or Middle.. I will usually take whatever is available when the parks are crowded.
It wouldn't matter on a coaster like space mountain.
Sincerely,50 year old coaster fan.