I think I would pick Kobe in his prime over LeBron in his prime, because Kobe has that killer instinct that LeBron lacks. LeBron is probably more physically gifted than even Jordan, but he seems to lack that killer instinct.
I also think the idea of a big 3 is terribly flawed. The Spurs showed team basketball is how you win. Team offense with passing and movement is far better than isolation, clearing out for your star player. The Spurs brand of basketball is fun to watch. Hope other teams emulate it.