My opinion is that the market is saturated with plenty of skimmers that perform well. The performance difference between skimmers that are in the low mid range to the highest end is minimal.
There are differences on build quality, ease of maintenance, longevity, parts, availability, support, and ease of adjustment.
What I look for in a skimmer is an external pump. External pumps are easier to remove for cleaning and easier to upgrade if you need to in the future. Space saver models take proprietary pumps and suffer in performance because the reaction chamber is smaller to accommodate the pump.
I like gate valve water level control. Many skimmers now use a wedge pipe which is easy to manufacture but 1 half turn of a wedge pipe goes from completely open to completely closed while a gate valve has about 3-4 full rotations between opening and closing. this makes fine adjustments much easier.
I also would look at the pump. The pump is the only moving part of the skimmer and it is the biggest factor in price. The pump should be high quality but also easy to find replacement parts for since this is the most common failure point.
Because of all of these factors I really like the Reef octopus INT skimmers they have a proven track records and all of the features I mentioned. I also really like the tunze master doc skimmers for the same reason.
Many skimmers that are considered high end actually don’t have these features. BubbleKing, Vertex, and Deltec all have poor US support in my experience and many use wedge pipes not gate valves. Not to mention that parts availability is no where near as good as with many other brands.