[Myka]

Since you didn't post a budget, I'll go all in and say the Abyzz will be top choice with a 10 year warranty. I'm assuming you do not want to spend over $2000 on a return pump though, so I digress...

For DC, I vote for the Ecotech Vectra. Provided you're not wanting to run a UV sterilizer on your return line, or a manifold, or any type of reactor. The Vectra doesn't handle pressure well, so it's best used in straight-run situations. These are handy if you want wireless control and connectivity with Ecotech or Neptune products. This pump will be over $600. Reliable? Not sure, they haven't been out for long.

For AC pump, I also vote for Sicce for the size range required. They are adjustable in the sense that there is a built-in valve on the intake basket to control flow. The pump itself is not controllable. These pumps are silent and reliable.

Assuming your sump will hold around 30 gallons of water which will offset the displacement of the rock in the tank, assuming you're going to have about 5 feet of head pressure, assuming it will be a dedicated return line (no manifolds, reactors, etc), then I would suggest the Sicce Synchra 5.0. The 5.0 will barely have you covered though, you'll probably be looking at about 4x turnover through the sump with that pump wide open. That would be my preference - I don't like choking pumps back. The next step up is the 10.0 and that's going to give you close to 10x flow through the sump wide open which is much more than I would want so it would need to be choked back, plus the 10.0 has a bit of a hum - it's a pretty big pump. There's a 50% price jump between the two as well if that's a consideration. This pump will be under $300.