I see this as a can of worms just waiting to be opened ;) Anyway, I'll say it before anyone else does. There really isnt a "best" scout class. They all do different things, have different jobs, and they do them all pretty well.
The Rogue path (swashbuckler/brigand) is a nice balance of utility, and DPS. You get a lot of fun abilities, and can dish out the damage over extended periods.
The Predator path (ranger/assassin) is high damage output, with some utility.
The Bard path (troubadour/dirge) is good damage, with a lot of utility, and group function.
Of all of these you really can't ask which is the best, for everyone is going to have a different opinion, people are very protective of they're chosen class, and we've yet to see the end game.
Also realize, that the game will go through many changes, and balancing acts in order to create a more balanced world. So even if there is one class that is better than another, it will either be hit by the nerf bat, or the other class's will be given other advantages to even out the playing field.
Play the class that looks fun to you, do the best you can, and you won't fail.