I've got a G&P M4 Special Operations. Can't fault it to be honest. Brill for CQB and outdoor games. It comes with a couple of bits and bobs, though I've taken the scope off of mine.
Let me know if you need any more advice around it.
I'm based in South London and would like to attend more MILSIM type events. However, not really had chance to get around to it. How easy is it to take your gear abroad?