There are no hormones or GMO in the chicken meat you get from the store in the US. I know you did not mention hormones but they have been banned in chickens (not beef or others) since the late 1950's. GMO is just not economical, they don't need it. They can do what they want through selective breeding. Antibiotics are a different story though they are tightening the restrictions on those. Still, I refer to grow my own veggies and chicken.
You basically have three choices for meat birds. There are benefits and issues with each. You can manage the time of year when you raise the Cornish X and Rangers so you can avoid the extreme temperatures.
The Cornish X are the most economical, especially if you buy all the food they eat. When you butcher them will vary a bit depending in what you feed them and just how big you want them, but that's the chicken at the store. Some people do pasture them but typically they are butchered really young, often at 6 to 8 weeks but pastured or restricted-feed can go a bit longer. These chickens grow so fast they need to be butchered before they have medical problems. They grow so fast their skeletons may not keep up so they break down or their heart just can't keep up. They are tender enough that they can be cooked any way, including frying an grilling. One downside is that they have to be butchered when it is time. Do you have sufficient freezer space? Will you have the time when it is time? These can get big and will probably give you the most white meat.
Then you have the Ranger type. These don't grow quite as fast as the Cornish X and are designed more to be pastured. These are typically butchered 4 to 6 weeks later and can pretty much be cooked any way, though some people might find them to have a bit of texture if you fry or grill the older ones. They can have some of the same medical problems as the Cornish X but not as young and usually not as severe.
Then you have the dual purpose. These do not get anywhere close to as big and cost more per pound of meat for feed. You are generally restricted as to how you can cook them because they are so much older before they put on a reasonable amount of meat. The big advantages to these is that they can reproduce if you want to breed your own and they don't develop the medical problems so you can put off butchering if you wish. From your goals I don't think they would suit you.
My suggestion is to raise a small batch of Cornish X and see how they suit you. Then raise some Rangers and compare. I don't think either will be a mistake for you and you can decide for yourself which you prefer.