Based on what do you say this?
Renfroe's OF profile seems to be - okay range, strong arm, and error prone. In totality about a slightly below average MLB RF.
Happ's OF seems to amount to a slightly above average MLB LF, and below average CF and RF, but can also play other positions. The fact that he can play 2B though, seems like something that would be appealing to other teams and increase his asking price. We do not need someone who can "also play 2B". Richie Palacios can also play 2B.
I guess it really depends on where we want them to play. I'd rather Happ to play LF and Renfroe to play RF.