As much as I disliked the guy (mainly because he usually played for *the other* team), I would have to say Chris Chelios.
In his prime, he was without a doubt one of the top-2 defensemen in the league. Multiple Cups, multiple Norris and a spectacular 2-way career. Leetch was better offensively, Chelios made up for it defensively and by being a stand-out leader. Not that Leetch is a bad leader, he just doesn't come with Chelios clout. Example, after the Nagano disaster, Chelios acted like the perfect leader. He apoligized for the incident and pay for the damages himself, but didn't rat the guilty teammates letting them take responsibility for their own actions. I don't know how somebody could have dealt with that situation better. Lafontaine is a great player too, but he didn't have the success (in terms of awards) or longevity of Chelios.
Gotta be Chelios for me.