Taste and texture a very individual preference and, in my opinion, is influenced a lot more by what age they are butchered than by breed. They all taste like chicken to me. The differences in tastes by breed is something else I can't help you with.
The Cornish X are generally butchered at 6...
I don't believe there is any one breed that is "best" for all of us for meat. What traits do you consider to be important in a meat bird. For some people it is size. Some want the best size at a specific age. Some prefer more dark meat than white. How much does egg laying matter to you...