Kean is probably the GOP's best shot, but he's not really a good candidate. His 2006 run stunk. He's not exactly the best Senate Minority Leader the state has ever had, either.
Guadagno is the Lt. Governor, but her name recognition is zero and her position has no real power. The position didn't even exist before she took office in 2010.
My dark horse pick would be State Sen. Jennifer Beck of Red Bank. She's still fairly youthful and enjoys a lot of local crossover appeal. She could play well statewide.
I would say two years later, Guadagno and Beck would be the best choices for the GOP. I could see these women being president one day.
http://www.njleg.state.nj.us/members/bio.asp?Leg=351