I think all 4 are really good.
Gonzales is only 18 years old and when he is in the batters box, he looks comfortable and he takes really good swings at pitches he should attack!! I can’t say that about Garcia or arias.  
arias has a lot of rafeala in him. Sometimes arias swings at pitches a a foot outside the strike zone. And ok, I admit, Gonzales gets fooled occasionally and swings at pitches a four outside the strike zone too! But where Gonzales will lay off the next pitch with that exact same spin a foot outside the strike zone. Arias will swing at it again and again !!!
I watch Garcia at bat and I do not know if he recognizes spin on breaking balls. I wonder what happens when he faces a nasty major league slider or cutter or sweeper!! He looked completely overwhelmed in spring training. That being said however, throw him a fastball below the letters and look out!!!
Campbell to me is the best pure hitter in the system, but he was rushed through the system and the major league pitches found his weak spot! I have no doubt that he will return smarter and better prepared next time. The problem is he had no defensive position, DH or outfield may work best for him, we have to keep him off the dirt.