LAgg or TAP- which is more +EV???

I just got poker tracker, and w/ default settings I am classified as a LAP. Which leak would be a better to work on first/most important??( Loose pre flop or passive post flop?)

Loose Preflop. When you are just starting out there is no better way to help your game than to tighten up. That allows you to, usually, make money while you work on your post flop game.

Preflop you should be folding most hands to raises and limping in with very few hands.
e.g. KJo in LP is a decent limping hand with no raises before you. You should fold it if there is a raise before you though since the raiser likely has a hand that dominates yours. If he holds AK, AJ, KQ, KK, or JJ and hits a K or a J then you will be calling/betting on all streets and will be owned. You want to avoid any situation where you are dominated when you hit TP. So limping in with no raise is OK but you need to fold it to a raise.

Definately the pre-flop play. You can't be successful with LAGG unless you have solid post-flop play. The easiest way to correct both is to tighten up your starting hands and the raises you're calling with them.