Personally, my favorite pick for governor at this point is polling even lower than Colbeck, Dr. Jim Hines (see his stands on issues here). Both lack the name recognition you need to score good on these polls.
Lt. Gov. Calley is counting on Gov. Snyder's questionable accomplishments, which may work in a primary, but definitely not in a general election where 'change' will be the motif in November. Schuette, Trump's pick, has shown himself to be a swamp creature through his career, and he's not changing anytime soon-- again a poor choice in a 'change' election cycle. So if the Republicans want to win, their two current poll-toppers are not likely going to be their best bet, unless the Democrats go nutty.
Hines meshes with my gears better, and I think he could appeal more to independents and disgruntled Democrats than Colbeck who has already made some controversy.