1. Voltages that are all within spec and remain there under all loads
2. Full advertised current capability, especially on the 12v rail(s), with low electrical noise and ripple
3. Quality PSU components that will last years under 24/7 use
Everything else is of far lesser importance such as how pretty the box is or if the cables are modular, etc. The trivial items may be importance to some folks but your PC could care less about this stuff as long as the three criteria above are in place.