I have both. I see them as totally mutually exclusive. If I had to get only one though, it would (unfortunately) be a trainer. On rollers I can get a good zone 2/3 aerobic (subthreshold) workout and work on pedal stroke efficiency and fluid pedaling. But on a trainer I can do threshold intervals and high intensity anaerobic sprints to the point of almost puking and passing out (sort of). I would find this impossible on the rollers. But if I just rode the trainer like the rollers with no structured workout I would go completely insane. Doing a Sufferfest video or Spinnervals helps me to actually push myself to the brink and actually makes it somewhat enjoyable. So, like I said, if I had to choose one it would be a trainer. You can still do lower intensity aerobic workouts on it as well as technique stuff like one legged drills and super high cadence work but I don't think it would be practical to do super high intensity brief intervals on rollers. . .at least not for me. I have not used the e-motion type of rollers before but from all the videos I have watched it seems like they would allow one to cheat a bit and get a bit sloppy on technique--more upper body movement and choppy pedal stroke. I suppose one option would be to get a set of rollers and use them standard alternating with putting them on the e-motion setup possibly with an added resistance unit.