I ditto on the AquaClear 70 ... I started with one on my 55g, but have since added a second. Most people will agree that there's no such thing as overfiltration (other than the high water current), so you can always go bigger than what you need. If you go smaller or right at the proper size, you can always double up on your filtration, assuming you have the space to put another on.
I can't speak for canister filters, other than the research I did while considering getting one. I was looking at a Rena Filstar XP3 for mine and if I remember correctly they were around $100 when I was looking last year. so, i have no idea what kind of maintenance, etc goes into those. I know you get some additional flexibility with canisters in taht they usually allow you to "hide" your filtration under tank in your cabinet, they usually have ample space to add bio additives, inline heaters, etc. But that comes at a price versus the hob
I went with the AC
70's based on price, and I love them. I think I got mine for around $25 each. You can still add bio-media / charcoal if you wish. My biggest argument for the AC
's are you don't have to keep buying replacement filter media. I just open mine up, and rinse out the sponges (I use 2 instead of just one), put them back in and its ready to go.
So, if you buy something like an AquaClear hob
filter, you'd have to decide what size you want ... given that you're thinking of transferring your new filter to a larger tank. Even if you went with an AC
70 or smaller ... you could use it as part of your filtration on the larger tank (ie: you'd need to add another filter in addition to the AC
I don't know how many filters others use on their large tanks, but my friend who has a 125g uses 2 hob
AquaClears and a canister on his. Now, could he get by with one good sized canister? I dunno ... probably.