These are the two teams that will give him the best chance to win more Super Bowls. I think 18 and 87 will try and reunite wherever they go, and Miami gives them a good shot at that. Miami has a solid defense, already has Brandon Marshall, and will give peyton a chance to win several superbowls. The only downside is that they are in the same division as patriots which will make it tough.
Broncos are another team with a solid defense, they have Demaryius Thomas at WR already. Also, John Fox is an excellent coach and they would immediately be a SB contender with peyton at QB. Also, they are in a very winnable division which is one edge they have over the dolphins.
I cannot imagine another team that could compete with these two teams to get Peyton.
Personally I think he goes to the Dolphins, he has a place in Miami and they are familiar with the city, Reggie is there already and I think peyton and reggie reunite in miami.