Neither is best. it all depends on your play-style.
Sorcerers are for more tactical players who devastate their enemies from afar, dealing great damage. also, they heal the players around them, making this a long-range DPS healing tactical wizard.
On the other hand, Assassins are for the more aggressive warriors, dealing MASS amounts of damage in zero to none time. they are preferably a tank class that gets up close and personal, dealing mass amounts of damage with their lightsabers. also, they are a stealth class.
If you are looking for more DPS, Assassin is the way to go.
If your looking for a more tactical prospective, Sorcerer.
On a 1vs1 battle, a Assassin would win most of the time because of their speed and high damage. in a team battle, a sorcerer is the overlord and will usually crush an assassin.
It is all about your play style.