You’ll probably get more use out of thief than Assassin. Since you are using big weapons you won’t get sneak attack bonuses, so the auto crits in surprised enemies might not be as useful as the mobility you can get from 2 bonus actions or all of the uses of enraged throw or frenzied strike if you go berserker.
Berserker gives you special bonus actions. Thief gives and extra use of bonus action. Natural synergy there.
