Hi,
We have used both the CPR and the Marine Life Aquatics unit. We have found the CPR's to be very reliable as long as they are used in conjuction with a venturi powerhead to stay primed. The MLA do not need the venturi pump, but they are also a "J Tube" style overflow. They typically do not flow as fast versus the CPR units, but they are less prone to collecting air bubbles in the top of the syphon. For a return pump it really depends on what you want to do, if you just want to drop in a single elbow return or run it through a SCWD, or Seaswirl, etc. Let me know how you plan on putting it back in.