I know several people here at AA use the Vortex diatom filters (I think they make two models, D1 and X something...XL or XS???) and like them a lot. My understanding is that they require more in the way of priming to use and maintenance than the other options out there.
I have the System I Pressure Filter, which I like because it is super easy to use (no priming) and you just hang it on the back of the tank, like any regular power filter. All the others need to go on the INSIDE of the tank while they are working, I think. There was also one called the Whisper Diatomagic filter that is supposedly easier to use than the Vortex models, but you do have to submerge the whole thing in the tank to use it. I haven't seen the Whisper mentioned anywhere for awhile, though. I am guessing they still make it, but I'm not sure.
The only problems I initially had with my System I were leaking and noise, both of which were solved by using vaseline around the lid of the jar and on the moving parts where the belt is.
joy to the fishes in the deep blue sea
55, 30, 30, 20, 10, and 10-gal. freshwater tropical tanks