Unless I heard Vogelbach was about to put himself through some strict dieting and off-season workout program. I simply cannot trust a player that out of shape. He's a few more cheeseburgers away from being out of baseball soon. He looks awful... Seriously.
I trust him about as far as I can throw him. (Yes, that's a fat joke)
At least with Marwin, he's consistently above average and you know you're getting some production that you can depend on. He also switch hits and plays every position outside of catcher. Reasonably durable. He'll always find his way onto the field nearly every day, for any team.
both are not great keepers... even in a 20 or more team league...
so the real answer is who cares!!!
but if you HAVE to keep one of them it would easily be Marwin.... But that is simply because of his position versatility... you can start him in multiple positions, and if this league is so deep that he is one of your keepers, then it would be nice to have options...