Valbuena has started 11/12 so far. Valbuena hit .224 last year, and is hitting .189 this year. He has 41 plate appearances, meanwhile Marwin has 20. I'd personally like to see that number flipped. I think we have a good idea who Valbeuna is, a decent 3rd base option, a solid fielder with some pop who Ks a bunch and isn't good at getting on base.
Meanwhile I think Marwin has a shot of hitting 280+, with 18+homers. Seems that Marwin's versatility is holding him back, he switch hits and plays multi positions, so he is a great late inning option.