I usually go by the combs first since even with hens some have larger ones than the others. Then I go by the size, feathers, or something that stands out about them in appearance. Last I go by personality. We use to feed the chickens old eggs. Only had a problem with a black langshan hen that would try to break eggs in the nests once in a while. Well one of our RIR's at the time would run over if you held the egg in the air and start jumping up and down begging for the egg. She would also follow you around when collecting eggs and try to peck them once you had it in your hand. Wouldn't touch them before but once you lay a finger on the egg she thinks it is hers to eat. Also have some that are more tame than others. Just have to observe your chickens for a while and then pick up on the differences. I've been able to tell most of mine apart and I've had RIRs, White Leghorns, RIR/Leghorn mixes (look like a fatter Leghorn), Barred Rocks, Black/White Langshans, Cochins, and a few other breeds that we had only a couple of each type.