There are lots of threads on this subject if you search for them.
I historically used a fluid trainer for a number of years and then went to a Computrainer when I got serious about riding and racing. That was many years ago when I actually got excited about spending all night in the garage racing 3D opponents on a dusty computer screen. These types of trainers can be very effective in my opinion but it does depend on what your objective is, not to mention requiring significant amount of discipline.
This last fall I purchased Kreitler rollers and now I never really touch the other types of trainer I own. The rollers are significantly better in terms of improving form, pedal stroke, balance, etc. You can add resistance devices if you wish to increase the level of physical exertion. Rollers are more engaging and for me the improvements gained on them translate more immediately to improved performance on the road. I often ride mine on a high deck that provides a good view and generally gives me a steady breeze to keep cool (not a good idea to start, would be bad to fall off!), sometimes I almost forget that I am on the rollers. Last note on rollers from me - fixed trainers I never used except when I could not ride outside, rollers I use even now for recovery rides or additional mileage when I don't have time for longer day rides.