Vera-Monson should be the fight right now.
Monson hasn't done that much more than Vera though. Vera has 3 UFC wins compared to Monson's 2. Beating Assuerio Silva is at least if not more then equal to beating Marcio Cruz. But with AA/Sylvia 3 at UFC 61 the HW title won't be defended again until November/December. And Monson and Vera will both have to keep active in the meantime. But then again you might not want them to face off against each other in the meantime since you don't want to eliminate any potential HW contenders unless you have to.