Rossi.

[Migv6 le Frog Fan]

Three weeks ago he fell off a dirt bike and snapped both bones in his lower leg, needing surgery to put it back together.
Today he has just qualified third on the grid for tomorrows MotoGP race.
At 38 years old, that's close to superhuman imo. 

[Field Marshal Dr. Opti]

Impossible to compare one generation of riders to another but I would put Rossi at the top.

'Fast Freddie Spencer'.....Ago and Hailwood would also be up there. Sheene good but not great.

[Shackeng]

Geoff Duke for me.

[BazaJT]

The riders have access to the best medical people/facilities in the world,but even so they all seem to "repair" quickly from some very serious injuries[Guy Martin is a prime example breaking his back and a week later back at work repairing trucks].Rossi himself has never claimed to be the GOAT but did rate himself in the top 5.With his antics after wins,one off colour schemes on bike/helmet/leathers he has moved forward what Sheene began in making the sport more of a show for the spectators.I think apart from the fact he still enjoys racing that he's after his 10th title to put himself 3rd in the championship wins stakes-and along the way breaking Agostini race win record.