If you are willing to shell out the bucks for an ETSS skimmer, you wont be disappointed. When deciding on whether or not to go with a downdraft you must consider the pump aspect also. No whimpy powerheads here; you will need an external. That will take up additional space, and (depending on which one you get), they can be noisy.
I'm using a Ampmaster 3000 on my ETSS 600 Pro, and it works great. The Ampmasters are very quite also. (Put a mouse pad under it, or buy the $12 anti-vibration pad).
Downside: Big, external pump.
Upside: Most commercial aquariums use downdraft for the finest water quality (see what your LFS has in the backroom). Dismissing shades of grey, it's pretty much the king of reliable, efficient skimming.