XM8 since the ROF is really good and the recoil is almost on par with the F200. Plus with the XM8 you can hit some hood headshots. The bloom on the XM8 lets you shoot the body up to the head, perfect for headshots. The F200 has a single spot fire. So if you cant aim you cant win.
I've always been disappointed with the F2000... just never performed better than my XM8 in any situation, whether it be CQC, mid range, or long range. I've actually never seen anyone use the F2000 in competitions, but I see many Para users switching over to the XM8 to use competitively. That says something, doesn't it?