I have both red and black sex links. In my experience they are both excellent layers of large brown eggs. The reds may lay slightly larger eggs although I find the quality of the BSL eggshells are better. The blacks are better foragers and eat less but mine are flighty and quite unfriendly. They are better fliers than the reds and try to escape their enclosure at every opportunity. They don't like to sleep in the coop with the others if they can help it either. My reds are very friendly and I can pick them up easily. I would pick the reds over the blacks every time given the choice.
Yes they both lay brown eggs and lots of them. I agree the gold sl's are really gentle and the blacks are a little more stanoffish but I haven't had any that were bratty or really mean. If you want to see sommting testy you watch some of them ol' barred rock hens. I think some of them got an extra little dob of testosterone every now and again.