To me it depends on what someone considers to be the most "athletic" and/or what is the toughest athletic "skill" to have and/or master.
Speed is a skill. So is endurance. So are jumping ability, strength, and hand/eye coordination, just as examples.
So what makes the best athlete? Someone who is the best in the "toughest" skill? Or someone who is well-rounded in most or all of them?
Arguments can be made on both sides of that debate. Bo Jackson may have had speed, strength, jumping ability and even some hand/eye coordination, but I'd bet the ranch that Lance could have beaten him in any endurance event. Does that make Lance the better athlete? I'll leave that debate to others.
But, in my opinion, Lance is the greatest endurance athlete of his generation - and it isn't close. Does that make him the best athlete? I don't know. But I know he belongs in the debate.