I don't think a fixed trainer really helps your form. Get smart rollers for that. Ride with good form or scare yourself silly on every ride.
I have my trainer on a rocker plate with fore-aft motion. I like it, but I'm not happy with how the fore-aft reacts when I stand up. Then again, I used to stand up mostly because I was uncomfortable, so that has been fixed. Really hard to do an all-out sprint sitting down though. My max power is 25% less.