Okay, so Outlaw does have the biggest damage potential, and is overall more initial damage to my own experience. It does seem like the overall go-to spec in all seriousness. However, Assassination does have its uses with Shadowstep, crippling poison and deadly poison. What this spec lacks in damage output, it has in utility. Both specs are viable, but played differently. However, if I were to pick one as the most powerful, I'd go with Outlaw, just due to the sheer damage output.
When it comes to talents in Outlaw, all of them seem viable. Quick draw has the biggest burst potential if Saber Slash procs the free Pistol Shot. However, it is inconsistent compared to the other talents. Swordmaster makes the proc chance of Saber Slash go up by 10%, so that's 35% to 45%, which is roughly a proc pr. 2 saber slashes (EU math
). This seems like the most sustainable talent, and doesn't require you to set anything up. Ghostly Strike definitely has its uses. Where I can see Ghostly Strike being good are in situations where you wanna land a kill on someone in mid with your team, or setting up a kill on EFC. I personally find that the go-to talent choice would be Swordmaster, just because it's good overall, it's not a niche pick, and will always give you some value no matter the situation pretty much.
Personally I find assassination a lot more fun to play.