Alejandro fulfills a necessary, albeit boring, role. He won't win, he'll make it decently far, but will not win. He'll either be outschemed or ganged up on once it's revealed he's evil.
Sierra is completely boring. Many people knew Heather was evil, they simply lacked the ability to vote her off, when other stuff happened, or she was invincible. Action had her simply working. I don't see her as playing Heather as anything special.
In truth, I would like the finale to be Courtney vs. Tyler. Courtney has abandoned her derailment from Action, and is now back to being simply obsessed with being a leader. Seeing as how Team Amazon is doing well, she's doing well on all the challenges, and having her specifically butt heads with Gwen leads to interesting things. She has the Gwen/Duncan vibe of being on top of things, and extremely capable, yet with her flaws.
As for Tyler, he's the underdog, in every sense of the word. He's the Owen/Beth, the sympathetic player who, unlike the other two, gives it his best, he's simply bad at it. He also lacks Owen's obnoxious characteristics and constant fart/fat jokes, and Beth's stupid geekiness. If you wanted a lovable loser, this is it.