Thank you for all of your replies. We were leaning rooster because of the difference in tail feathers, the developing red comb/waddles, and his bolder disposition (he will run right up to us while the others are still a little shy).
My wife and I recently ordered 15 chicks from Meyer Hatchery and one of our Buff Orpingtons is standing out from the other 4 (1st pic). The others look like the one in the second pic.
Any help/thoughts on what sex the first chicken is would be greatly appreciated