It really depends on play style, and seeing as you said you're new, it's best to give both a try.
Or if you're still leveling from 1-10 do you find yourself using force lightning and standing at distances from your enemy, or do you end up using thrash and staying within melee range of your enemies?
Go from there, would you like to stay within melee range of your enemies, and have stealth abilities to get that better chance of attacking someone unseen or would you like to stay at greater distances and generally channel things?
Another thing to consider is that assassins have the option to tank, meaning they can live a little longer and protect people who heal them.
Sorcerers can have the option to heal, keeping your team alive, while also running away from people who will eventually target you.
Myself I have a tank assassin in gear intended for damage (not so much protecting). This helps with surviving longer and also doing a good amount of damage.
I really like Force Lightning but inevitetably get charged and have to Thrash I'm used to tanking but don't mind variety.