Rollers are my preferred indoor torture device. Trainers make me suicidal. Nothing removes any joy from riding a bike more than locking your back wheel into a rigid stand and pedaling for an hour.

That being said, it's easier to link computers to trainers, so most of the ride simulation systems use trainers.

On the other hand, I can do intevals just fine on my rollers, thanks, and the element of danger keeps me awake/aware of the task at hand.