I got my ones from here:
http://www.piggottspoultry.co.uk/meat.htmlDepends how you want to manage your birds really.
The white ross/Cobb are the most popular boilers. They grow super fast. Not very good for free ranging (although will manage).
The other "breeds" of boilers grow slower bit have no problems with too fast growth (heart attacks, joint and bone problems).
I've had Ross Cobb and red boilers together last year. When they were in the brooder, I.e. not exercising too much, the white ones were growing faster but when they were outside free ranging, the red ones were doing better!
Unless you prefer some pure breed chickens?
Ross will take 6/7 weeks. Red boilers up to 12. Most pure breeds will take several months longer and probably never grow to the same size though.
I have Poule de Barbezieux, poule de Bresse and am ordering more red boilers (very pleased with them last year) and some naked neck boilers to try.
As for flavour, Ross will have the least although if they are on grass they will still be MUCH better than shop bought chicken.
Hope this helps