I had a friend who had an AK-47 (guessing it had been modified to be civilian legal as it was semi-automatic fire only), he let me fire it a couple times. I know a lot of people like them, but I could never get used to it, just felt "awkward" when firing it. Felt "too short", can't explain it. When it comes to rifles, I'm used to shooting Lee-Enfield's and they are a World apart so that might have something to do with it?
When it comes to modern military firearms...I'll have to stick with the M-16A2 as that is what I had (minimal) experience with. The M-16 just "feels" more "normal" when shooting it, hope that came out right? Then again it was been the better part of 15-20 years since I fired a real M-16A2, so that might feel weird to me as well.
Mark