There are a lot dumb, thin arguments tossed around when it comes to this debate, including from so-called experts. The two dumbest, imho, are "six for six" and "ten Finals." (If you at least go on to elaborate on the significance/meaning of "6 for 6" or "ten Finals," then maybe you're saying something worth hearing.)
A person could probably write a hundred-page essay on either side of this debate, yet most commenters attempt to defend their position with a few sentences or a handful of stats.
Which is (kind of) what I'm about to do.
Prefacing by saying I could probably write that hundred-page essay if I wanted to spend six months working on it, I'll now try to summarize in just two reasons, or ten minutes, 
the essence of what I believe made Michael Jordan the greatest to ever play the game. It won't be better than this: 
 but it's a small part of what I can add to the conversation at the moment.
Reason #1: Shot-making. 
In an era when space around the basket was at a premium and contact was the norm on the perimeter, Michael Jordan could create a high-quality shot for himself or a teammate, from any spot on the floor, at any time, in the half-court. One of the most convincing arguments against LeBron James in the above video is the knock on his shooting 
outside of 3 feet: 35.9% for his playoff career, and not much better in the regular season. This hasn't hurt him as much as it might have, because he's played much of his career in an era when: 
a.) it's been relatively easy to get to the rim, and/or 
b.) greater emphasis on the three has increased every player's ability to be mathematically efficient from outside while not necessarily being a very good shooter. 
The last game of the '96-'97 season, which the Bulls lost while going for their second-straight 70-win season (MJ scores 33, not 65, lol), is a good example of the kind of shot-making Jordan was capable of even at the age of 34. Look at the shots he's taking/making, and then realize he shot 14 of 22 from the field in this game. There is no gameplan for that. You simply hope. One major difference between MJ and LeBron is that when you were hoping MJ would miss from outside, you were hoping for a much more unlikely outcome:
Reason #2: Mentality. 
In the NBA, Jordan never had to learn what James finally learned in Boston in 2012, because Jordan had learned it before he got to UNC. This is maybe what some people are implying when they say "six for six" - as stupid as that argument is on its face. I could name a few other mental areas where Jordan excelled James (psychological domination of opponents and fearlessness when a miss would mean a loss, to name two), but suffice to say that Jordan almost never had a playoff game where you could say "they lost because of him," and he certainly never had a series like that. James had two such series while in his prime. 
Everyone is familiar with his unforgettable 18 ppg on 
48/
32/
60 splits with 7 assists and 
4 TO's per game in the 2011 Finals. Perhaps worst of all, he only took 15 shots per game and only shot 3 free throws per game in that series. 
Lesser known, but arguably just as bad, was his total, personal collapse over the last three playoff games of his first tenure in Cleveland. These are James' numbers over the last three games of that series, as he "lead" the 61-win Cavaliers in three straight losses to the 50-win Celtics, giving up a 2-1 advantage to lose the series, 2-4:
21 ppg on 
34/
15/
74 splits. 8 assists and 
6 TO's per game. 
Astonishingly bad. This was a player coming off of back-to-back MVP seasons, who had reached the Finals before, and whose team had averaged 64 wins in the previous two seasons. This was not a youngster still learning the ropes of the NBA playoffs. 
And while I'm here, though we usually give him a pass because he was young or something, it's worth remembering James' numbers while getting swept in the 2007 Finals:
22 ppg on 
35/
20/
65 splits. 7 assists and 
6 TO's per game.
Brutal.
Michael Jordan doesn't have a single blemish on his record as bad as any of these, never mind 
three such blemishes. Whether it was because of his superior shot-making ability, or his tighter handle, greater mobility, and better control of the game, or his tougher mental makeup - or, all of the above - no one ever saw Jordan neutered in that way, and that speaks volumes about the gap between he and James.
 
            
                                    
                                    All human life on the earth is like grass, and all human glory is like a flower in a field. The grass dries up and its flower falls off, but the Lord’s word endures forever.