Originally Posted by
Thassarian
Basically, Watchman is a bleed spec, you get Cauterize up on a high uptime, if not 100, get healed for every time it crits as well as the ability to kite/bleed someone to death. Wheras Combat is a more physical spec, you rarely use Cauterize, it's only just better than a Blade Rush/Strike on overall damage as you don't have the points to go deep into Watchman as well as pick up Blade Rush.
Combat's DPS is better when the target doesn't move and better yet, when it isn't attacking you. Watchman's damage is better if the target doesn't move, but you're still doing your damage while the target is at a distance (dots). It's a matter of preference; I never quite liked Feral Druids in WoW so I'm not a fan of Watchman spec, while I've played Fury/Frost/Ret/Combat and raided on all of them so I associate more with Combat.
Focus is the shared, mostly, pvp spec for JK's. I don't know how good it is in PvE and I'm unlikely to try it considering most of the abilities and talents are to do with control, as opposed to both of the other specs focusing on DPS.