I'm using a toms aqua lifter, only does a few gallons an hour and I've seen quite a few reefers w them, they get a bad rap though on reviews but I haven't had anything to complain about yrt
What are you using that didn't come with a pump already?
If money is not a huge concern here I don't think you can beat the spectrapure UPLC-2.
If you are using some sort of float switch setup you can just buy the peristaltic pump part of the UPLC-2 which is just awesome you can pull vertically from 25' or push vertically up to 60'. This pretty much means you can place your ATO reservoir anywhere you want. The one I have on my 60 cube now pulls from a basement room 1 floor down on the other side of the house.