Both Mag and Fluid are much, much quiter than Wind trainers. Mag pretty much stops when you stop pedaling - no coasting at all. Fluid, on the other hand, does roll some with your movement, allowing you to stop pedaling briefly and then start up again without having to fully pump back up to your former speed from scratch (which more accurately conveys what you'd feel on the road). If you just want to work out, either would work. The fluid ones are nicer, but not necessary.