rollers...
i have both. I live in Ontario, Canada, where the winter is long and inhospitable so riding indoors is a necessity. I had a trainer for several years and just got a set of rollers last winter.
I use the trainer for long sessions (over 1.5hours) or for intervals. I use the trainer for long sessions because I can watch a movie (to distract myself from the fact that I am getting nowhere fast) while on the trainer and for intervals because I can easily adjust effort. On the trainer, I would for sure get an indoor-trainer-specific tire (hard plastic, no traction on the road but really durable for the trainer).
I use the rollers strictly for spinning and for warming up (before doing strength training, etc.) and not usually for more than 1hr, maybe an hour and a half. I say this because the rollers (at least for me anyways) need more concentration.
I cannot watch a movie while on the rollers, or have my children around otherwise I am at risk of losing balance and falling off, It's strictly the ipod and my spinning legs . I also find it harder to do intervals on the rollers for the same reason, risk losing balance when changing speed, standing up... The rollers are A LOT of fun though and great to develop/maintain your core. I credit the time spent on the rollers last winter with better handling in slippery situations (ice, mud..).
hope this helps. good luck in your shopping around 
julie
2013 Parlee TTi, campy athena carbon, 3T cockpit, fizik ares
2012 Cinelli Strato, campy chorus, edge/enve cockpit, fizik vitesse
marinoni fango, sram rival, fizik vitesse
miele tournet, converted to SS, white and pink fizik vitesse