Single. I did rebase for a while with 2 x 2 figures per base but decided against it as 48 fig battalions were taking a while to build especially when I am a gamer 1st and painter last :)
I am using Empire V basing so the bases are for 15mm figs and historically accurate although I have them a little deeper to handle uneven terrain better but the width of 120mm for a 720 man battalion in line of 3 ranks is accurate for 180m in real life.
I am using paper strength units and regiments so whatever battle or campaign I play the units can be adjusted by only fielding a portion of the stands and for regiments only a portion of the battalions.
So for French I am doing all regiments with 3 battalions of 720 men or 12 stands of 24 figs. That way for Waterloo I can take 1 or 2 or 3 battalions for the Regiments and anywhere from 6 to 12 stands where needed. All cool stuff.
Same for the Allies with 12 stand battalions except for some of the larger units and elites such as the Guards battalions with their 1000 men at the beginning of the campaign.
For Prussians I am working on 720 man to 900 man units or 12 to 15 stands per unit. Need to do more research here though before I settle on these.
Also with the larger number of stands I can do all formations especially the narrow road columns and british attack columns. :)