These threads are always amusing. Everyone has their favorite.
Personally I think that you should got to a pet store or two that carries those filters. Open up the box, take a look at all the little pieces and read the directions. Buy the one that you believe you understand how it all fits together and will be the easiest to maintain. When I bought my first canister, I did this and when the clerk came by and raised an eyebrow I just pointed at the price of buggers. I then went home and bought it cheaper online...
Or if you are on a tight budget like me you'll lean towards the least expensive one.