I voted xp3 also, though I am running Fluvals at the moment, first ones I've tried. I used AC
filters for a long time, but recently switched to cannisters. Learned about them on this forum! First on one tank, then on all my tanks. You can fit alot more filter media in a cannister, you can inject C02 directly through it, you can do that with an AC
filter as well but it's way more effective through a cannister. Lastly, you can easily adjust the amount of surface aggitation you get by lowering or raising the filter output, plus you can direct the current easy by aiming the output wherever you want more flow in the tank. Love my cannisters, the water is crystal clear as well.