Take a look at the Skimmer comparison chart. Granted, this page hasn't been updated since June 2008:
http://aquariumcontrollers.com/aquarium-equipment-comparisons.php
There are several kinds of skimmers on the market.
Beckett (Trigger Systems, for example)
Needle Wheel (Euro-reef, ASM, Octopus)
Mesh Wheel (MSX, some tiny Euro-reef skimmers)
True Venturi (Sea Clone, Prism, CPR Bakpak)
Spray Injection (Aqua C - EV-series, Remora, Urchin)
The "best skimmer" discussion is an arbitrary one. It comes down to how much money a person paid for theirs, and how much they want to defend that purchase. Also, the bioload of the tank can have a huge effect on how well a skimmer works or won't work. If the skimmer is massively oversized for example, the owner may be completely unhappy with the lack of results. Using my giant skimmer on a Nano tank is a good example. In theory, the skimmer works perfectly but the lack of waste in the water would imiply that my skimmer doesn't work correctly due to a lack of skimmate.
If you have a 300g tank, you need a skimmer that can skimmer 300g with a heavy bioload. In that case, I'd be looking for a skimmer that others really like, and I'd probably seek a skimmer that can handle 350 to 400g ratings-wise.
The newer Cone skimmers seem to be able to handle larger tanks with smaller footprints and with less electricity. I'd love to try one out to see if it is true, but for now I'm not really shopping for a skimmer. What I have works. It's a Euroreef CS12-2 with two Eheim pumps using needle-wheel impellars. The skimmer cost me $800 back in 2005, and I just replaced both pumps this year at a cost of $400. My skimmer is rated for 500g. My system is around 350-375g total, but the actual water volume is very likely around 255g.