I have both. I own an Orion 2500D and a Sundown SAZ-1500D and I could tell you a few things about them from a repair/amp tech perspective.
Orion 2500D: Very powerful, high current output section. Has lots of reliability issues with age, buy new or less than 1 year old IMHO. Expensive repair bill, lots of parts, lots of labor
Sundown SAZ-1500D: Also very powerful, more than a 1500 watt amp, it's a little underated. Higher Voltage output section than the Orion. Very good reliability, less weight, less space taken up, looks as good. Not as powerful as the Orion 2500D, but much more reliable design, way less repair bill if it breaks, about half the repair bill of a 2500D.