I'd take Marte. He's expected to steal 40 bases this year and could also hit 16-20 HR. Brown & Marte both had around 170AB in the majors last year but Marte stole 12 bases Brown 0. He also had 5HR. so those projections are realistic.
I would go with Brown, but I've always been a believer. So far this spring he's killing the ball. Marte has equally impressive potential, or at least close, but I think he's a year or two off. That average is a problem right now, one that I don't think Brown will have. It's just a gut feeling, but I'm going Brown on that one.