Fluval internal filters only have small sponges and need cleaning all the time. Eheims aren't much better. Aquaclear powerheads can be fitted with a "Quickfilter" attachment and this can be used. However, it has a fine white filter cartridge that is useless so you need to replace it with a cylindrical sponge from another type of internal filter. Aquarius internal filter sponges fit nicely inside the Quickfilter cartridge.
The other option is to go for an external filter like a canister or hang on back (HOB) filter. These have more filter media and provide more filtration with less maintenance.
Internal Whisper Power Filter, you can get at Walmart for cheap. I have three and they work great and are so quit you don't even know they are running. Only thing I don't like about them is they take up room but for the tanks I have them on I don't have any other option.
Fluval are good filters, but they have small filter sponges that clog up quickly, meaning more work to keep them clean. In fact most internal filters have small filter sponges and big pumps, which is really the wrong way around. Due to this arrangement you need to get a big unit too get a reasonable size sponge, and the big units tend to blow the fish all over the tank. Some companies have been working this out but most still make big pumps with small filters.
Depends on tank size; I ran a Fluval 4 Plus on my 4ft tank for two years without any problem. It had two large sponges (with space for a third, finer sponge inbetween). I'd imagine when you drop down to the 2 Plus and the 1, then they'd be much smaller sponges. The new Fluval 'U' internals are out now, so you may find better deals on the old 'Plus' internals as shops try to get rid of old stock.
Personally I like my Interpet PF2 internal PowerFilter, doesn't take much cleaning, (perhaps once a month), and runs almost silently when you have the venturi switched off, (even with it switched on you only get the bubbling noise!)
Of course, bin the carbon filters straight away, and put something else in instead. Depends on what fits, but you can always cut floss to size.
Having a space for carbon loops is a great idea.
Another option for internal filtration is a nice big sponge filter with a small power head. That way you can get the right proportions that Colin T was talking about wanting.