HOB style filters take up space on the outside of the tank, whereas internal power filters take up space inside the tank.
The advantage of AquaClear HOB filters is they have a wide area where the water flows out of the filter. This means there is a current but it's not as strong as a jet of water from an internal power filter or external canister filter.
Having a bigger (not too large) AquaClear filter will mean the water flow will be higher but also spread out over a wider area. And if you ever get a bigger tank, you can use the bigger filter on it. Or you can transfer one of the sponges into a new filter and have an instant cycled tank.
All AquaClear HOB filters have the ability to vary the flow. If you put a cylindrical sponge on the intake of the filter, it will reduce the flow a bit more.
That was me. I really like canister filters, because they're dead quiet (even the cheapo SunSuns I always get), have a lot of room for media, allow one to move a LOT of water without creating excess current (by using spray bars), allow one to customise exactly where the intake and outlet is (this is important to avoid dead zones in the densely 'scaped tanks I like to build), and don't take up any room in or behind the tank, since the whole thing lives in the cabinet underneath. @Fishmanic is right though--you can't beat a HOB for ease of maintenance. Cleaning out a canister is a pain in the rear.
As for the overfiltering "myth": Ah, I do love it when the common wisdom is challenged, even when I happen to agree with it. I myself have successfully kept (female) bettas in community tanks on several occasions; I've successfully mixed "tropical" and "cold water" species when their needed conditions overlap; all of my tanks use dirt substrates. All of these practices seem to go against the going line on this particular forum; none of them are practices I would necessarily recommend to a beginner (except dirt substrates, which are wonderful if you do them right). Often the common wisdom is a good general idea, but somewhere along the line it turns into holy writ.
So it is with the old double-filtration rule of thumb. I still think most filters are good for about half of their official gallon rating, especially for the densely stocked tanks so many people prefer these days. But your mileage may vary. This hobby has so many variables, there is almost always more than one way to look at things. You pays your money and you takes your chances!