I can't see much advantage of one over the other, it's mostly about personal preference.
Red SUPPOSEDLY can handle the heat better & that may be the case, but... my Red Angus cows (and they grew up a couple hundred miles south of here) live under the shade trees just as much as my black Lowlines. And going one step further, our black Tarentaise spend a lot less time under the trees than the Red Angus. I've also noticed no difference between black & red Tarentaise tolerating heat. Although there may indeed be a difference, I can't see much difference.
Somebody once mentioned that red cattle have less flies on them than black cattle... well, that's simply not the case.
I can tell you that the people who want red will only buy red, but for every 1 person like that, there are at least 5 -10 times more people who want only black cattle.
From the outside looking in... I do think that the Red Angus were selected a little more for the commercial person & the black Angus were selected a little more for "show ring" fads.
I managed a herd for a breeder who bought some EXPENSIVE show winning Red Angus females back in the 1990's & I have some Red Angus cows of my own right now. But, I've seen nothing so far that has caused me to become a big Red Angus fan. I'm also not a big Black Angus fan, although I do like the Ohlde genetics & I really like the Lowline Angus, but they are different types than the typical "Americanized" Angus.
I raise both 100% Angus (reds & blacks) & I raise composites. I can tell you with 100% honesty that the very best animals are the composites.
RE temperment, confirmation, size, finishing ability, and hair coat... that varies a lot from individual to individual within a breed. Since I know Lowline Cattle, I'll use them as an example...
Doc Holliday sires calves with lots of hair & fuzzy ears, but Tigers Eye sires calves that are typically much slicker. Doc Holliday sires really docile calves, but I am hearing that Quartermaster makes some of his offspring higher strung. Doc Holliday is almost 49 inches, but Quartermaster is only 39 inches. Bluey has an incredible marbling score of 80 something on the MMI test, but a lot of high marbling Angus bulls are significantly lower. So, as you can see, it's more about the individuals than it is about the breed.
I would guess that you can find exactly what you are looking for in Red or Black, Big or Small, all you will need to do is spend some time looking & then be ready to open your check book when you find what you want.
All the above is just my opinion, based on my own personal experience. I by no means know all the answers & I can be & I have been wrong from time to time. However, I sincerely hope that I've been helpful.