I'd like to see him polled against Alexander Mooney or Patrick Morrisey.
McKinley or Morrisey would be stronger. McKinley has been in Congress for sometime, although Morrisey has won statewide before (and alongside Manchin). I don't think Mooney will run, maybe a few cycles later when there's an open seat and he gains experience in the House.
Mooney won statewide GOP Chair in Maryland. He knows how to run a statewide campaign and staff it properly. He's younger than either of them, more energetic, and he is pretty moderate. Two terms in the House is quite enough experience for the Senate, in my opinion. In 2020, an incumbent Republican Governor and Senator are running for re-election. Should he hope to run for Governor in 2024, Senator in 2024/2026(if Capito retires after two terms/McKinley retires after one term), Governor in 2028, or Senator in 2018? Pretty obvious choice to me.
Carpetbagger Mooney is the one person Manchin would have a chance at beating.
Are you just a Democratic hack?
Mooney is actually well liked and pretty young. Just because he moved states doesn't make him an automatic HP. Mooney is by far the most moderate of the three. IIRC, all three Republican Representatives are in the Mainstreet Partnership, so they probably won't be any worse than Capito. Capito and Manchin are two of the best Senators in the Senate, IMO.