I went with Machida, since he's undefeated and has what it takes to be champion. Oh, and I'm a huge Ryoto fanboy. While Jardine, Forrest, & Alexander are in some odd triangle, Machida's 3-0 in the Octagon.
But, if I had to choose between Forrest, Houston, & Jardine, I'd choose Forrest. Sure, Alexander hasn't been defeated in the UFC yet, but Forrest is coming off an impressive win against Shogun. Also, Forrest has charisma, is exciting, and can cut a promo. A Rampage vs Griffin fight would be fun stuff.