Black Powder is my choice at the moment but looking DBN to see if that ha any potential.

I normally fight solo using Kallistra hexagon terrain, modelled and modified.  I have developed a generic simple set of rules for 1700-1950 with modules for each major time period, but don't use them much nowadays.

Here is my list in descending time order:

1936-1945: Memoir44 adapted.  Rapid fire (testing), Battlegroup awaited, Homegrown.

1900-1920: Homegrown, Great War awaited.

1880-1910: Rules for the Conduct of the War Game

1790-1815: Commands & Colors Napoleonics, "Est-il hereux" (an eclectic "pre-Reisswitz" game for display at reenactments - available from me on demand)

1700-1715: Now normally played in 2mm, otherwise homegrown rules for 6mm.  Will try C&C for the next outing.

1630-1650: Period largely ignored nowadays, except in 1830mm scale. Various rules tried and all abandoned.

Black Powder works well, you need an enormous board for 28mm, so 6mm on a 4'x4' board is great. Basing wise, artillery is 2 guns, this allows for half batteries if needed (in some of the campaign books). 6 stands of 8 men for a regular bttn, again easily allows for formation changes and size variants. Cavalry 6 stands of 3 for the reasons already given.  Oh and skirmishers I put two men to a stand for mixed order etc....

Am just starting a napoleonic Volley and Bayonet project; have used the rules a couple of times and quite like the simplicity of it.

Rank and File for ACW, AWI and Napoleonics. Spearhead for WW1 and WW2. DBA 3.0 and Swords & Sandals for ancients. Principles of War for all periods. 

Age of Eagles, Age of Honor and now Regimental Fire nd Fury for those "Big Unit"  down in the dirt games,

AoE/AoH use 2-3 bases  per regiment (I use 3/4 inch by 1 1/8 inchwide) with two strips of infantry or 3 Cavalry figure per base.  An Inf base is around 400 men or a bit more, while a cavalry base is around 240-300. An Artillery base with 2-3 figures and a gun is a single battery. This is for games between Armies...whole Armies, Like Blenheim or Malplaquet.

RF&F uses a 3 figure base representing 40 Infantry, 2 figures of cavalry is the same I think and a gun with crew represents a two gun section. Some of the regments can have a LOT of bases (like 36-42 or so) and that isn't the Austrians either. Geared to the ACW, some secarios for Napoleonics have just been released. I'm thinking a base as described above with 8 figures (two strips) will make a good base in 6 mm.

Jim

Black Powder for Napoleonics.

I'm currently basing a bunch of Dark age fellows for Dux Bellorum

I use Age of Eagles. It's based for 15mm but works well with 6mm. I use the same base sizes just add more figures per base.

Ancients - Scutarii

Currently getting started with Bloody Big Battles