Mainly DBA and its other period offshoots...DBA-RRR, DBN, DBA-ACW, etc.  Also DBM with 100-150 points.

Getting into good old Phil Barker's WRG 1950-75/83 for "modern", I had these rules when I wa sin college in the early 1980s!  I have yet to find a good set of WW1 rules that I can bear reading through.....War Times Journal's may be the best and least convoluted. (Free online)  John

I will be trying To the Strongest for ancients, and I have been using Black Powder for Napoleonics at 1/3 scale, 4 x 20mm bases per unit.

For 6mm:

Napoleonic - General De Brigade

ACW - Fire & Fury

Depends on the period and game scale. For AWI I use Black Powder, but for WSS I use Horse, Foot and guns. Ancients; DBA, and DBR or Pistolero for Renaissance  (incidentally, can we have a good C16th range sometime?). For WW2 and Modern; I haven't done these as miniature games for ages, but I had forces for WRG rules, or Blitzkreig Commander, and AK47 Republic for African Wars.

GWSH2 - not actually Polemos. Also use Square Bashing for a quick evening game.

If I ever get round to colonial Sudan  I may well use For Queen and Planet, Principles of War C19th, Science versus Pluck, Patrols in the Sudan, or FOB2. Sussing them out at the moment.

Great War Spearhead II, INEPTT, Pony Wars, Flames of War (but not in a long while).

Maurice for 18th century

ACW  -- Altar of Freedom and They Coudn't Hit an Elephant

Ancients -- Chipco / DBA

Vietnam -- Charlie Don't Surf

WW2 -- I Aint Been Shot Mum

WW1 -- Great War Spearhead II

Planning on 1866 and 1870

Ancients: Hail Caesar, Basic Impetus, Sword and Spear, Warmaster Ancients (no clear favourite has yet arisen)

Napoleonics: General de Brigade (acquired and planned for a russo-swedish war project but I need to paint some figures first)

ACW: Fire and Fury, Black Powder, Volley and bayonet. (Now looking for rules to reignite the love)

WW2 (20-28mm): Chain of Command (I have a big crush on this right now), Battlegroup Kursk.