If you can only get one machine, get a good fluid trainer. You can do everything on it, from endurance riding in front of the TV to anaerobic threshold intervals.

That said, I have both. I do endurance riding (up to 2 hour sessions, and yes, while watching TV) during the winter exclusively on the rollers to enforce good pedaling form and smooth bike handling. I do interval sets on the trainer.

FWIW, talking about warming up at races... people tend towards trainers because it's easier to throw into the car and it's hard to find flat ground next to your car door sometimes. At the track, in contrast, you'll see almost no trainers in use for warmups. Only rollers. Myself, being a bit of a trackie now, I use rollers to warm up for pretty much everything. I have 3.25" rollers on it, so I can get to near threshold without resorting to a resistance unit, and it gets me more "in the game" than plowing along on a static trainer does.

Another option is e-motion rollers. I don't have one, but I've heard good things, including that you can just about out-and-out sprint on it without worrying about balance anymore than you do on the road. Not terribly portable though.