[Tubbs]

I recently picked up a Rock River Arms M-4 lower receiver. Initially I wasn't interested in an M16 weapons system or its ilk, but I got it for a good price.
As a Marine I have only had hands on experience with the M16A2 and I have never actually fired a genuine M4.
I know what the gun rags think are good systems, but I was wondering what the rest of you have personal experience with? I would like to know what the professionals on this site think is a good M4 upper.
Another thing that I would like to know is what accesories, if any, you think would be good to go along with it. Don't get me wrong, I'm not a "gear queer", but as a Marine we didn't get the good toys to play with. I prefer to get some reliable personal references before I make a firearms accesory purchase. After all, my life may depend on it some day.

Also, on a tangent, I would like to say thank you to the adminstrators of this site. This was my first foray into the world of forums and it spoiled me. I recently attempted to venture into some other forums and was... well, underwhelmed by the quality control. This is a well moderated and intelligent forum. Again, thank you.