I have a knock-off version of a Tetra 10 on my 6g, seems to work well and moves the water a bit too well when turned all the way up...
Although, I don't have the experience of many people here, so going with a 20 may be better for you.
the ac 20 is a good bet for you as the flow control will be beneficial. i have both an ac30 and a terta 10 on my 10 gallon at home. the tetra filter uses the bio bags which pretty much only have carbon on them, the filter is good for catching finer debree but doesnt allow for you to customize your media like the ac's do.