Best? what is most important to you?
There are a lot of different things to consider, flow rate, cost, ease of cleaning, silence, mechanical filtration vs biological filtration, ability to add different media, reliability in the long run, dependable restart after power off, cost of media and replacement rates.
I like Penguin for a reliable restart after power off, the 330 (now 400?) lets you add extra media, and all have biowheels for extra biological filtration. Good flow rate, moves water but not overpowering. Not too quiet, but if you keep the water level up it is not too bad, seems to evaporate more water perhaps. Reasonable price online, you can use refillable clamshell type frames instead of the expensive cartridges to save money by cutting padding to fill the frame yourself. Can get extension to lower intake. Not flexible as to outflow. Never overflows onto the floor. Too much surface movement for a planted tank with CO2 injection.
I like the HOT Magnum for the optional micron filter, though I usually have the carbon basket filled with Efisubstrat biomedia. Reliable restart after power off, slightly more flexible in directional flow, extension for intake available online. Very quiet for a HOB. Never overflows. Not too expensive, don't know how long lived it is but all of mine are used and are fine. Tricky to reassemble, keep extra gaskets onhand, you will tear one eventually. Fine for CO2 injected tank.
I have had several Whispers, a bit noisier than some, but they were used so maybe that was why. May run dry in a power failure and then not prime and burn out the motor when power returns, often needs a finger poke at the impeller to get it going at startup. Not great as the only filter on a tank but fine as a second filter.
I had one Millinium2000, interesting concept with the biomedia frame but really noisy as it seems to inject air.
I babysat some fish that had a little AquaClear, very powerful flow on them it seems. That means that mechanical filtration is better than biological filtration. It required a poke to restart and I've read that if it is not cleaned it can overflow onto the carpet, did not observe that myself. Larger units can hold various media. Sponges last a long time, so ongoing costs are low.
If you have this in a bedroom or a planted CO2 injected tank, I'd prefer HOT250. If you have the room on the tank, don't mind the noise, the Penguin is very good especially if you are new to fishkeeping for I think the biowheel cycles faster.
