I like to tell people to take the rating on the skimmers and cut it in half. That is the max size for efficent skimmer use.
I used the old model prizm. It is a bit louder than the Remora for example. Sensitive as Brad said in adjusting it but overall its a good skimmer for the price. The new models include the ability to use a surface skimmer. If you get the prizm get the surface skimmer attachment as this will greatly improve the skimmers effectivness.
You could even go one step further and DIY
yourself a skimmer.