neither they're both Benders... hahahah, nah just kidding but i remember Sven Bender being the better one. but if you could get both, then you'd have two good midfielder, who will get along immensely.
I believe Sven is a little cheaper and has slightly better defensive stats(marking and positioning I think but could be wrong), but Lars has better pace and first touch. I have Lars as DM on my Arsenal team and he has been stellar
Lars is better, if you compare the attributes everything that Sven is better than Lars at, Lars is already boss at that anyway. Sven's wages are considerably less and would cost less. If you're playing 2 DMs then they would probably go very well together, stick Mario Gotze in the AMC position in front of them and you have a quality German midfield my friend.