Oh please not another AK vs AR debate
That can take you years to figure out. I will say this, for close range combat, AKs may prove superior, but for longer range combat, an AR will be essential, as an AK is not very accurate. I personally think purchasing an AR-10 with .308 round will be much better investment than an AK-47. The .308 round is superior to 7.62 x 39, more penetrating and retains accuracy at farther distances.
Check out DPMS and Armalite.
If you got the dough , you may consider investing in an M1A, its a real sweet gun, but may set you back couple - few grand.