Some teams have the lucky bonus of naturally having colors that go well together. Dark blue and orange is a great color combination that generally works no matter how much blue or how much orange you use. Those colors mixed with the awesome bronco logo make for a lot of interesting combinations that work well. These designs don't shy away from using the bronco logo.
The top right includes the rocky mountains, which is great for a painting, but might be a little too busy for a football helmet. In my opinion, the bottom left design uses the best mix of blue and orange, along with a large bronco logo. The people in the nosebleed seats won't have a problem seeing the logo.