Don't you just love when Costner goes around the building and approaches the bad guy holding the damsel. He just walks up to him and shoves his gun towards him as he pulls. My now favorite Western.
Looking like I got my first choice of gunfight correct from all the replies. Heat is second or tied. Sure there are many others as we read on.
My favorite part: Right after the first shooting, when the bad guys scatter, Costner picks up the head bad guys rifle. (Only guy smart enough to bring a rifle to a gunfight!) Costner starts by putting another shot into one of the bad guys on the ground, who was only wounded. Never leave a live enemy behind you!