I hear good things about both Aqua Clear and Eheim. Eheim is especially praised by users, but is also the most expensive. I've never used either brand personally.
On my 10g tank, I use an internal Fluval U2 filter rated for tanks 12-30g. The tank is always understocked and doubles as a hospital tank. It uses sponge filters as opposed to pads, and has worked out very well for me so far. The decision to use it was more a matter of not having any clearance above the back half of the tank than anything else (sitting on hutch). Normally I don't use internal filters due to the tank space they take up.