Romero is a silver medalist as an Olympic wrestler, so his pedigree is elite in that aspect. He is also very fluid in his standup,utilizing a complete arsenal of knees, kicks, and elbows. He also finishes most of his opponents, so he isn't a boring , point fighter. His best win was his most recent (Tim Kennedy), so Machida will be his toughest test to date.
Romero is 38, so this is probably his only title run opportunity. He simply cannot afford to lose to Lyoto.
Machida has to look to finish this fight. As a counter striker, he usually does not do enough work to win a decision outright.
Like Rockhold, I expect Romero to be the bigger, stronger fighter, but Machida is a step up in competition.
If I had to guess......I think Romero will wear Machida down, and tko him.