I think that performance wise they are on about the same level. Although I do hear that people say that the Shocker is somewhat more accurate (although that is anothr debate all together), and there are way more possibilities for upgrading a Shocker. The Bushy beats the Shocker hands down on the efficiency area though, it uses far less gas.
Another marker in that range you may want to look at is the Matrix. Sweetest trigger of the three, although they are a bit of a gas guzzler too. Something that the Shocker and the Matrix can, is work on Co2. For a Bushy you'd need a compressed air syatem, which ofcourse is way more expensive to buy than a 20oz Co2 bottle.
Hope this helped.