If you are going for the best egg-layer...and your eggs are all the same...you could use a 'trap' nest to know which one laid which egg and keep track by chicken and select her eggs.
For the meatiest, you could keep track of weights as they grow (assuming you would want fast growth so they can go into the freezer asap from hatch...then breed those? (I guess if they are in the freezer they won't be breeding--- lol, maybe someone on the meat boards could give help there??)
For my chickens, each has a different egg color, and their body types are different too....so it is very easy to know which is a good layer, and which will produce plumper chickens.... And good egg laying is a thing I will always be selecting for (among other traits)
good luck.