This comes down to your team's needs. I personally would opt for Castillo seeing as he plays at a shallower position. You are right in that both will put up similar numbers. Both have perpetual green lights to steal and the way the Marlins are playing, Castillo's run production could be equivalent to playing at humedored Coors.
Agreed. If positional scarcity plays a role, give a (slight) edge to Castillo, assuming he keeps playing at this level. In terms of overall numbers as well as potential for the future, I like Pierre a bit more.