Before it was .20's were the best, then it was .25's, now we have .28's?
Keeping on this pattern we'll have .30's or .32's becoming the "standard" weight eventually.
Brandwise, I'd just but one of everything and test them out. See which company you like and run with them.
I actually bought some Firepower .25's the other day and I know one thing for sure, I'm not getting any more of those. (Didn't feed properly in my rifle, or my buddy's PTW, and had chopping issues). Also they're seamless on the outside but not very seamless when we cracked one open, and they had air bubbles and all that.
As of now it looks like I'm either going to be running BB King, Bastards, or Metal Techs exclusively. Testing them all out ATM but I can tell you one thing is that to not get Firepower.