SpaceX

Honestly, I don't think this could have gone any other way. As the article says, this is the so-called "Lane 1" missions which, while they're less important and less heavy than "Lane 2" missions, are perfectly suited to the Falcon 9, or heavy if needed. There's no need to get a heavy rocket like Vulcan involved, especially since it's not proven yet, so the only reason I could think of for someone else winning would essentially be as a subsidy to help SpaceX's competition. Once Vulcan has a couple dozen successful missions under its belt I'll expect it to be more competitive.