I have a Juwel filter column in one filter - it's basically a square tube full of sponges with a powerhead at the top. Excellent for biological filtration, excellent for fish who like still water like angels and gouramis, absolutely crap at producing current for fish who like that, like minnows and guppies. It's also very useful for stuff filter floss and sponges in to mature them - I could go into business producing instant cycling media (i.e. used sponges from my filter)
However, it takes up a lot of space IMHO.
On another tank I currently have a Fluval 3 internal filter. It's a little over-loaded but the tank is planted so provided its producing current for my guppies, it'll do. The main benefit to old-style Fluvals is that they are dirt cheap 2nd hand. They do contain a sponge but its only one measly little sponge.
Another tank has a Fluval 2 - same idea only smaller. It's normally the back-up filter on the tank with the Fluval 3, but I think it's possible to have
too much current.
Finally I have a box filter, filled with dissected Fluval sponges and filter floss (from my Juwel), running off an air-pump. Surprisingly effective for a 12 gal tank, considering how cheap it is.
I'm saving up for an Eheim external filter to replace the Juwel one. Eheims can have anything you like in them - I'll probably use the sponges out of my Juwel and some filter floss, since I'm not convinced fancy stuff is necessary. Besides, it saves cycling a new filter.