What if i did just buy 1 of each?
I'd go with the Aquaclear. The seal job on Toms are usually quite poor, so water leaks and sucking in air are pretty common complaints with it.
the only place I had issues with the one I tested was the tubing.
I used some Aquarium sealer(silicone) and sealed the fitting on the canister and it functions fine.. the only draw back is it really is only suitable for a 10.
but personally with aquariums I prefer 2 filters.. one on each end.
a 20 g filter really is not suitable for that size tank .
you could run over sized but with 2 filters you reduce 'dead' spots in the tank.