I only got to visit Camp Perry for a few hours last month (just to see it and get the t-shirt), but I had very similar questions and every time we would stop to try to find friends, I would just start asking shooters around me what kind of equipment they were using (among other things). Most of what I found was an amalgamation of different parts, but there were an awful lot of Bushmaster upper/lower combinations there. I only talked to a couple guys shooting RRA rifles and of all the vendors, RRA was the one that really pissed us off. It seemed like everyone had Krieger barrels on their rifles, you would see other names too but what really surprised me was that there were several folks shooting with the Bushmaster DCM Match barrel. As far as triggers go, Milazzo seemed to get a lot of respect, but it’s my understanding that they aren’t available at this time. People seemed to react like Superman to Kryptonite if you mentioned Jewell.
I was only there for a few hours on the day of the Presidents 100, but got to talk to about 30 different shooters and some various salesmen and gunsmiths. It really sounds like the best rifles are the ones that are custom built, not the ones coming from the factory; the manufacturers come up with a good baseline, but it can certainly be made better. That said, my sister wound up buying a new Armalite with the understanding that she’ll probable be needing a better barrel pretty quick.