All of the superstars in the NBA work hard. A 1000 shots a day, a strictly regimented diet, an hour of lifting and treadmill, autograph signing, etc. etc. is a normal day for these guys. We'll never truly understand how hard they work, especially from afar.
I love KG. I think he's one of the hardest working guys in the game. But I also think his big mouth draws more attention to him, at least on the court, than even a guy like Kobe would draw. We see how hard he works on defense because we're always trying to trace his bark. The same is true for offense.
I don't think anybody works HARDER than KG. But it's not out of the question to say someone like Kobe, who puts hours upon hours into skills he's already mastered and more hours on top of that into skills he'll never master (even at 34 years old), works just as hard.