After using multiple bottle ATOs for my Evo 13.5g and my IM Nuvo 10g, I got one of these:
On sale now at CoralVue
All-in-one auto top-off system for small aquariums under 50 gallons. The Smart ATO Nano Kit comes with everything needed for installation.
store.coralvue.com
I like it because it is simple and
just has a pump that gangs on the glass. I got a "nice" cereal container at Target as the ATO container because a dumb container shouldn't cost as much as a tank:
The lid makes refilling it slightly less tedious than the bottle, which involves taking it off, unscrewing it, filling into the little bottle opening (unless you've got a funnel, in which case you're too smart for this thread!), turning it back over and letting water spill out, etc.
Anyway, I like it.