I've had a set of rollers for a little over a year and bought a fluid trainer about a month ago.... The rollers are nice on recovery days (I don't have any resistance & they are large drum rollers), but good practice once or twice a week. The trainer gives a much more focused workout, I don't like doing intervals so much on it, but putting myself in a well focused zone 2/3 workout is time well spent. The fluid trainer is much nicer to warmup on at races also.
Since you own a trainer, but a set of rollers, used if you're short on cash. I paid $20 for mine...