I use a fluval u4 filter?i think that's what it is!its an in tank filter,the ones out of the tank/canister ones seem to come highly recommended,I'd say buy the best filter you can do that if you end up getting a bigger tank you can move the filter over and it still do its job.
I might be talking rubbish it's been a long day but when I went to buy mine the guy said if I ever got a bigger tank (mines 220l) I'd need a canister filter because the one I got only does up to 230l.someone else might be able to explain better what I'm on about!