In my estimation, there are few if any bad skimmers left on the market. This means that almost no matter what you decide on, the skimmer you bring home will skim.
"To skim"
as we've come to understand, means the removal of around 30% of organic material we add into the tank in the form of food and some additives. Sadly, there is no magic involved.
What this means to Revhtree's thread is that no matter how much you spend, your skimmer is still going to play by the same rules of physics and at most achieve around this level of performance.
Having said that, it seems there's a dizzying array of skimmer choices on the market and a decision can be hard to make!
YMMV, of course, but here's how I'd recommend deciding:
First, consider history. All our commercially made skimmers originate in
a design from Germany. Our needle-wheels are only a significant evolution (also from Germany) of these designs. Since then, there have been some innovations here in the US - predominantly downdraft and spray injection by AETech and Aqua-C.
That history, in fact, is a pretty accurate summary of what's on the market today. Of the US makers, Lifereef still has an excellent Venturi skimmer (any others?). AETech and Aqua-C are still both around with their air-mixing technology and have solid options which both allow you to choose what pump you want to run. Tank already overheated? Use something more efficient (and more expensive). No heat issues? Get the most durable pump. (Etc.) Euro-Reef (now Reef Dynamics) are the ones who brought the needle-wheel+volute induction to the US and have very consistently offered awesome, well-designed skimmers (highly effective, easy to set up and maintain) for pretty much every size of tank. These days they even make nano-size skimmers. As mentioned, there are a lot of good skimmers on the market, but these guys are (what's left of) where it started here in the US and collectively they still make an excellent place to start your skimmer search. After these guys you have every skimmer copyist that's come along the pike - some literally making identical copies in China from a molding of one of the above maker's skimmers, some using weird shapes and pretty colors to differentiate. Personally I recommend supporting someone in the US that's actually doing R&D and manufacturing here just because I/we live here in the US. If that's too pricey for you to consider, I'd suggest to either use a savings plan (old-fashioned, I know) or buy used. Both are good options!
The biggest secondary factors to consider in my opinion are ease of maintenance and how quickly the skimmer fouls its reaction chamber with "Skimmy Peanut Butter". (Mmmmm!) The worst skimmers in this regard are going to kill their own performance more quickly by fouling the reaction chamber/neck, and they're going to make things worse by making it hard/time-consuming to do the required cleaning. (Note: If you find snails and stuff living in your Skimmy, it's past time for a cleaning! LOL) The best skimmers account for these things and are easy to disassemble and require less frequent cleanings in the first place. With this stuff in mind I can say that in-sump is better than external; slip fit is better than thumb screws and wet skimming is better than dry skimming. (Indeed, wet skimming can make all skimmers better in this regard. And not that external skimmers with thumb-screws are bad, just that they wouldn't be my first choice!)
There are lots of good skimmers on the market and maybe even zero that are "bad", as I said at the beginning. If you "buy with your head" it's actually pretty hard to go wrong.
-Matt
