Barabas is our main man, but you don't have to like it. (Or him.) After all, he's basically a monster. He remorselessly kills the innocent along with the not-so-innocent, lies his way through basically the entire play, and, near the end declares "so I live, perish may all the world" (5.2.10).
But there are still moments when you root for him. In that initial scene where Ferneze is heartlessly destroying Barabas's life and livelihood, you really feel for the guy—Barabas is clearly being discriminated against and there's nothing he can do about it.
Another thing you might like about Barabas is his sheer will to live and keep going. Even though it's totally self-serving and unfeeling, that"perish may all the world" sentiment can be really appealing. The moment he stands up and dusts himself off outside the city walls is triumphant. However terrible he is, Barabas's persistence, his determination to defy those who "Think me to be a senseless lump of clay / That will with every water wash to dirt! (1.2.216-19) makes him our protagonist.