Robinho is by far the better player.
Skillwise, I would say that I have never seen a player who is better than Kinky. Some have been as good, though very few indeed - perhaps Le Tissier and Gascoigne from the nineties, and maybe Bergkamp in a different way. I'd say Robinho is probably his equal skill-wise as well, though he's a less flashy player.
But football is about more than just skill. For me Robinho makes far better use of his abilities, and plays the game more simply. He isn't always trying to beat his man or do some outrageous piece of skill, even though he could, because he recognises that the game is about making the right choices as well as showing the most ability.
As to workrate, neither of them were hard workers, which you wouldn't expect in their position. I don't really think there's a great difference there.
One last point: people are saying that Kinky had to play with some dross and his achievements are consequently more impressive. He did have to play with dross, in the first division. But that 95-96 side was nowhere near as bad, relative to the league at the time, as people are making out. Rosler, Quinn, Flitcroft, Lomas and Curle were all quite decent footballers (in Quinn and Curle's case at least, really quite good) for the league standard at the time. That team should never have got relegated.
It's just an opinion but for me there is no comparison: Robinho is a far better player. It's very sad that, for whatever reason, Kinky never became the world class player he should've been.