(SPOILERS)The gecko brothers from the "dusk till dawn" series have been through a lot over the course of 3 seasons. They are seasoned criminals that have become expert culebra(snake vampire) killers. They recently began taking on xbalbans (Aztec Gods) in the newest season. Richard is himself a culebra. He has enhanced strength and regenerative abilities as well as the ability to persuade his enemies through touch. Seth is an excellent fighter. Together they are a serious contender. They are somewhat easier to manage when separated.
The winchesters are legacies in an illustrious line of hunters and men of letters. They have been to literally been to hell and back multiple times and killed pretty much every monster you could think of from werewolves to witches and even the occasional god. Their greatest weakness however is each other. They often lose focus if the other is in danger.
So.. who wins???