rocks lay brown eggs, leghorns lay white (i have seen tinted but i don't think this is right) my experience with the both of them:
leghorns take less feed to make more eggs, have more trouble with comb freeze and don't lay well in the winter. also we do eat our birds and leghorns don't have much meat. they are flighty but if you keep them in a quiet place they do relax.
white rocks are one of my favorite breeds, nice brown eggs that get alittle lighter in color with the age of the hen, meat quality is pretty good on these birds. they seem to keep laying in the winter but they do slow down a little. add some light and usually this problem is fixed. my white rocks lay much bigger eggs than my leghorns.... and white rocks can go broody (if you want chicks)