I've seen very few using powershot, but when it works they do great. Glaive toss and barrage can both break CC which is a pain in arena, and their damage is similar, so not entirely awful. Use any of the 3, but remember powershot sometimes simply doesn't work.
Powershot in bgs as marksman can be amazing fun opening with aimed>powershot. The crits for ps are a nice piece of burst, but the fact that 50% of the time the shot never registers blows. In arena I use glaives for consistent and reliable damage.