For ultimate accuracy I have shot kegs and kegs of Varget in the .223, and to a lesser extent Reloader15 and H4895. These are stick powders that I throw short and trickle up to exact weight. Ball powders like 748, BLC(2) are what I use for good ammo that is not used in a match where I spend a lot of money to enter. I am 1/2 way through a jug of IMR 8208xbr that really performs well and is small grained so it meters really well.
I did have a very stout load of 748 that I shot in an early spring match very well. The same load on a 100+ degree day went unstable and I was piercing a lot of primers. That never happened with a less than max load.