Rangers have higher DPS than swashies/brigands (or at least they will after the upcoming combat overhaul), but both rogue classes have nice DPS as well. I'm not sure which is the best soloer. Rangers get better ranged combat arts (obviously) and more sneak attacks, while both rogues get more positional attacks.
Since any race can play any class, you can do whatever you want with race. Brigand is evil only, while the other two classes are good only, so if you pick a race of opposite alignment from your class, you'll have to do the betrayal quest. If you're just looking for races with high agility, halflings and half elves are pretty good...I think dark elves are too.