As far as DPS, Rangers have the highest DPS of all scouts, but if you are looking at highest hitting, its the Assassin. Rogues are pretty good DPS, but still don't quite match up to the Predetors. Bards are fantastic to have in a group for their songs, while not the most damaging, they are very helpful. Myself playing an Assassin, I can tell you that it is fun to hit in high numbers, and with high agility, if a mob that is white or below falls off the tank, I can take it by myself with no problem, at least at the lvl I am now. I would say as far as your question concerning if Assassins are the best scouts, if you are looking for pure DPS, go Ranger, but if you like seeing that you just hit a mob for 600+, Assassin is the way to go.