White leghorns, by far. My 16wk white leghorn started laying last week, and we've had 9 eggs in 9 days from her. Plus she's as sweet and friendly as she can be, but that might not be important to you.
I have 5 two week old RIR's, and I can't wait til they start laying so I can compare.
some of my production reds just started laying, and they lay good ol' big brown eggs, but my flock of 10 frizzle bantams, nearly lay on cue, and laythe biggest of any banty eggs i've seen! and they are one year old.
I say leghorns because I've only got one pullet laying right now, and she's a champ. Last time I had chooks, I had so many laying all at once that I couldn't tell who laid how many. I could, however, tell my leghorn eggs apart from the rest, and they laid more per bird. I never had a barred rock that lived to lay an egg (my one was killed by a dog), so I don't have that experience. I have 2 in the henhouse right now, tho, that haven't laid an egg yet because they're only 17 weeks old.