I'll disagree. I have mine in a tractor and move it. The smell is normal. If you take care of the bedding or move the tractor, the smell is not out of line compared to the layers. If you cram 50 birds into a small closet and don't clean up, yes they will smell horrible and look disgusting.
What is your goal?
Grocery store meat is cheaper. If you like large, mushy meat, done.
If you want taste, everyone says heritage breeds and older birds. They will give you a "normal" chicken carcass. Like the rubber chickens you see. That is a real chicken carcass compared to the Cornish Cross meat birds. It will taste stronger and be more toothsome. I like this.
If you want a lot of meat that tastes better than grocery store that you raised yourself quickly, Cornish cross is a viable solution.
The beautiful thing is you choose the correct answer. After reading all the horror stories, I read the stories of the people who have done it and are trying to improve by sharing solutions. There are many ways to raise chickens, dogs and kids. Which one is right for you?
As far as which breed is better, they are all made of meat, so try them all. Better is relative. I've raised Barred Rocks from a hatchery. Raising Cornish Crosses now. And will try broilers or Naked Necks next for meat. Best wishes.
PS. Whatever you decide, have fun doing it! That is the secret to a lot of things.