Here is a post from another thread:
Troops scales are as follows:
Infantry base (8 figures) = 450 men approx. (4 or 6 bases per unit)
Cavalry base (3 figures = 175 men approx. (4 or 6 bases per unit)
Artillery base = 6-8 guns approx. (2 or 3 bases per unit)
There's a range associated with each base, but the above is about average.
So infantry units have either 4 or 6 bases per unit. In the (very) draft playtest lists you could (just about always) choose whether to field 4's, 6's, or a mixture. Occaisionally you might be required to field a minimum number of small or large units. I assume the final lists will be similar in this regard.
My favourite army is 1809 Austrians, and I field line infantry in 6's, which helps them to weather skirmish fire and drive to close range - which Austrians need to do. Also the Austrians are not that maneouvreable and advancing straight ahead or defending, rather than tricky stuff on the flanks tends to be the modus operandi for the infantry. For about a third of my units I have only painted 5 bases as support bases will be attached to these.
Grenadier, Grenz and Jaeger I field as 4's, they are more expensive but specialised troops and 6's can be a bit expensive.
Landwehr I always field in 4's. I do not use them to fight but to provide rear support to front line units, defend the line of comunication against wide ranging enemy LC, garrison non-essential towns, and raise the army morale level. However if you intend for your landwehr to fight, then you definately want 6 base units.
Cavalry generally are better in 4's as small units more maneouvreable and can fit into gaps to (try) and launch combined arms charges better. However, if a single small cavalry unit runs into a single large one of similar type, it will almost certainly lose. An occaisional large dragoon or LC unit is therefore worth considering for operating on the flanks against enemy cavalry.
For the artillery, I like 3 base units as tthey allow you to concentrate more artillery firepower in a division. A large artillery unit is also more likely to stop an assault in it's tracks than a small unit. Andy, my most frequent playtester, however much prefers 2 base artillery units as they can pivot and bring new/better targets into arc more easily.
So to answer your question, I would generally go with 6 base large Austrian Line units, in 1809 at least. You can put either 6 or 8 figures on each base (I go with 6 per base, the author likes the look of 8 better).
With Bavarians, mostly 4 base small units would be my choice. Bavarians are more maneouverable than Austrians and small units maximise this. You also don't have the same issues with needing to get to close range that the Austrians have.
Generally, you need better Divisional Generals to command formations made up of lots of small units, whereas Divisions of smaller numbers of large units can get away with lower quality commanders.
Cheers
Brett