Give me MJ, if only because I can't think of any meaningful dunks Carter actually had. His game has historically been flash over substance, and I think his dunks are a reflection of that.
Over the last three seasons, Carter has dedicated himself to leadership and defense. If he'd shown that commitment early in his career, he'd be known as an all-time great, rather than just as a great dunker. Better late than never, but it's one of those "what might have been" things.