Boris all the way.

His PR and image teams are in the gym as we speak preparing for the contest.
No more buffoonery, no more poorly chosen off the cuff remarks. Maybe even a new haircut.

Who else has the gravitas?

I know that he dropped a political clanger with his conduct in the Remain group but I think that George Osborne is one of the few people with the gravitas to play hardball negotiating our exit

This Boris Johnson?

Boris Johnson wants to keep the UK's access to the single market and does not believe concerns about immigration played a defining role in the vote to leave the EU.

"There will continue to be free trade, and access to the single market," Johnson wrote.

"British people will still be able to go and work in the EU; to live; to travel; to study; to buy homes and to settle down."

- [Link]

I think it'll either be Boris or Theresa May. He'll go the EEA route, as he's said he will today, to settle the economy and say we'll look into how we can address the 'free movement' issue when we're on an even keel. He'll then do nothing and start making the odd promise about it again come the next general election. No referendum next time though of course.