What's your budget?

I'm using a Wahoo KICKR with Trainer Road and it is really a phenomenal tool. Also have a set of cheap rollers from Performance. I use them for recovery rides.

The KICKR has an erg mode that basically forces you to hit power or hr numbers for a set amount of time. There's nothing like that on my rollers (though I know that Inside Ride was working on doing it with some sweet e-motion rollers).

Look up the model of rollers you're interested in buying and look at the watts required to spin at various speeds. You will likely see that the top end isn't too high, and you can't actually do 30 seconds or a minute all out. So no HIIT. VO2 max intervals may be possible, depending on your model and your fitness. Rollers are great for form sprints, because if your spin is too bouncy you will lose control. It forces you to be smooth. When I first started on rollers, I also found my core getting a nice workout, which didn't happen on the trainer.

tl;dr if you have the budget for it, get the top-end e-motion rollers with an erg mode (if they're out yet) or something like the Wahoo or Powerbeam, or some other trainer that is "smart" and can communicate with a computer to vary resistance via bluetooth.

If your budget is in the 100-200 range, it really depends what you want to train: your spin or your sprint.

If you have 200-400, you should get a cheap trainer and cheap rollers too, because it's nice to switch between them.