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!