If your rating here is an accurate reflection of your playing strength, I'd be tempted to say "neither, play something simpler" . The Lasker defense or the Tartakower lines of the QGD are easier to grasp in terms of the ideas and given that either you or opponent will leave book pretty early, both of these QGD systems would be solid ways to deal with 1.d4 d5 2.c4.
One more advantage of starting with classical QGD is that you learn a lot by figuring out how Black fights in the Q-Side, how to resist clockwork attacks on your h7 / Kingside and the importance of break moves (...c5 being the most vital!).
These ideas help you transition to the slav-type stuff later on.
I'm studying both defenses for an upcoming tourney. I'm trying to determine which one is better and also which one is more appropiate for my playing style. I like to play really aggressively but I need a sound defence because I don't want to be too reckless.
Which slav do you prefer? Or if you don't care for slav's which defense do you prefer?
Any input is appreciated! :D