Grosskreutz is just a guy who's made a career out of working hard. Nothing wrong with that and he is a nuisance but the quality is not there really. Muller is pretty straightforward in what he does, but he is world class at it.
They're both pretty amusing personally but in different ways. Grosskreutz is your typical Dortmunder Jung standing around the Hbf singing stupid songs with his mates whereas Muller shows genuine wit dressed up and delivered in timeless Ober-bayern style. Muller no doubt appreciates the work of Gerhard Polt and enjoys the Harald Schmidt show whereas Kevin never misses an episode of Berlin Tag und Nacht over a well earned Doner. As for the other joker, Podolski, he relishes Tom and Jerry on Sunday mornings.