I have had all 3 types, fluid, mag and wind. Wind is noisy, mag is linear. Fluid seems to give the best road feel and not be windy. I own a fluid and will replace this with another when it bits the dust. The cateye wind/mag unit is nice. I had this one also, but it is noisy trainer
I use a mag trainer with variable tension (a cable goes from the trainer to the bars).
It works fine for my needs. I guess how much you might want to spend might be a factor.
The main thing about a trainer - no matter what kind - is to get yourself to use it. If you use it, I think it makes little difference what kind. Most trainers sit there unused as using a trainer is one of the most boring activities in life, especially for an outside biker.
I use training videos, which help me a lot. I happen to use Spinervals, but there are others around which some folks seem to like better ( www.spinervals.com ). It gives me a pretty intense 45 minute winter workout. I also use the Lifecycle at the gym just for variety and my wife goes to the gym with me.
Some folks swear by rollers. I would fall off and injure myself - no thanks!
My wind trainer was louder, but with 700 Watts of stereo I could hear the music just fine That is why I sold the cateye as the wife hated the thing. Like denver said, me I do not like the nowhere bike. That is why I use it so rarely now. I need to look in to those tapes though as I need something to break the boredom of the trainer.