We raised a number of breeds last year to compare the flavor. We probably let many of the males get too old, we raised them to 4-6 months, in general, but this is our general experience. Our favorites were Rhode Island Red, Speckled Sussex and Salmon Favorole, but many other tasty birds include Light Brahma, American Bresse, Bielefelder, Wyandotte and Marans. I do not agree that all birds taste the same. The Marans is moist and mild, the RIR tougher but super flavorful. We did not care for the Delaware, too mild, or male sex-links (we got a few freebies from a hatchery). We liked the Dorking, but it is a super slow grower. We definitely recommend resting the bird in the fridge for 1-2 days, and/or brining it O/N. Older birds benefit from a long slow cook. Coq au Vin is a classic French dish using a mature rooster. The older the bird, the stronger the flavor, but they do get tough, and need a long slow cook. Some chefs will hang a bird in the fridge for a week to age the meat.
This year we got more RIR, are raising some Marans and American Bresse, plus a few Sussex and are trying Basque hens. The Basque Hens are on the Slow Food Ark of Taste, but then again, so are the Cayuga Duck, which we think is OK, but not the best duck breed we tried.