For me, I look for a skimmer with a clearly marked optimum water line, and for the love of all things holy, a pump that is not inside the skimmer body.
I had a bubble magus that had an internal pump which needed fiddling-with fairly often, and I had to open the godddamn thing every time it got finniky, then the pump went bad and put 10,000,000 volts into the water, at which point I found out that BM knew of the problems with the pumps, but kept selling them anyway. So (for me) eff BM.
I grabbed a reef octopus and I swear to you, I've never had to clean the pump in the 4 years I've been running it. Just insane. I can't say that's indicitive of RO quality, I may have just got a real good one, but WOW the difference between the two products was awesome (the RO is way way better at dialing in your skim thickness too).
As always, that's just my take on it. If I had to replace my skimmer I'd buy a reef octopus again in a heartbeat.