Pogba could be to Juve what Ronaldinho was to Barca. An extremely entertaining and effective player that football fans from all over the world can enjoy watching and would tune in just to see what he is going to do next even if they are not Juve fans. Barca's commercial success is largely due to Ronaldinho's brilliance which gave the club an amazing marketing opportunity.
Keep him at Juve for 2-3 years. Let him build Juve a wider international fanbase (especially amongst youngsters) and make him the center of the team. Let him take the penalties, give him attacking freedom, make him the club's poster boy, publish youtube videos full of his tricks, praise him in the media, hype his price, sell his shirts, get him to have twitter sessions with fans and live Q & A sessions, campaign for him in awards, put him on Fifa's cover, get him to be awesome on Fifa and FM, Nike advertisements, get club legends to mention him in the press and praise him to the sky, get him to donate money for some cancer kids and make the press know how generous he is. This guy could be a commercial goldmine and if he goes to madrid his commercial potential will be overshadowed by that of Ronaldo.
When all that is said and done, then sell him for mega money to Madrid and rebuild your squad using his money and the much increased income level generated off his back.