I enjoy Eckmuhl enormously each time I play it. It has the greatest variety of really challenging medium-size battles. And then of course this gourgeous huge map with the 534 turn scenarios--operational warfare on a ground that perfectly lends itself to nice meeting engagements, ambushes, etc. Almost an adventure quality.
Waterloo is coming close, as far as I can tell; I haven't played it enough yet, especially not the smaller campaign scenarios, but the huge map is the best way to experience the 1815 campaign in my opinion.
Wagram is a really good game, but the battles are in many ways more conventional set-piece things. And there is no big map for the entire campaign. (Of course, both is no fault of the game, the campaign just was that way.)
For reasons discussed in a different thread on this board, NRC is the one I like least. Making tactical battles decisive in a campaign that was lost on the strategic level just isn't coming close enough to a credible portrayal of the 1812 campaign, and to make it work, the armies had to be given certain characteristics that don't seem historical. (Again, that doesn't mean that Charlie hasn't done a great job, given these circumstances and the limitation of the system.)
My € .02. [8)]
<center>
D.S. "Green Horse" Walter, Maréchal d'Empire
Duc des Pyramides, Comte de Normandie
Commandant la [url="http://home.arcor.de/dierk_Walter/NWC/3_VI_AdR_Home.htm"]3e Division Bavaroise[/url], L'Armée du Rhin
Commandant [url="http://home.arcor.de/dierk_Walter/NWC/EdM_start.htm"]L'Ecole de Mars[/url], L'Armée du Rhin
Commandant la Brigade de Grenadiers de la Moyenne Garde
</center>
