I like Marwin, I like that he's a switchhitter, but he doesn't field as well at SS as Lowrie does, and Lowrie is no plus fielder. He's 23, so maybe his bat will develop more. Lowrie is a legitimate hitter at short.
Lowrie's 28, and there are some good shortstops in the pipeline now so it's quite possible he's at his highest trade value here.