I have ViaAqua pumps. They are cheap, but they do a decent job (at least the smaller ones anyway). The bigger ViaAqua pumps really heat up the water, and I had one large one fail on me. I think you'd be fine with one, though. I currently use two ViaAqua pumps (one for my reactor and the other for my water changes), and they do fine.
As for what size, it depends on what your UV sterilizer recommends. Post the specs on your sterilizer, and I can try to help. Probably if you Google the type of sterilizer, it will tell you the recommended gph, and then you can pick an appropriate pump.