Over the years I have used various rules, here are the ones I currently use with my figures:
20/25mm ancients - WRG 6th (Considering using WAB)
6mm Ancients - all based as 15mm but with 4x the figures for DBA.
20mm New World - various skirmish sets, nothing settled yet,
20mm TYW - my own variant on DBM (before DBR was released) and tried the TYW version of Warmaster published by the P&SS US equivalent.
6mm ECW - all based as 15mm but with 4x the figures for DBR
25mm ECW - for 1644 or WECW
20mm SYW - my own rules (see Free wargames rules)
20mm AWI - my own rules (see Free wargames rules)
20mm Napoleonics - still trying to find to right set that provides the flavour of the period, uses big armies, but on modular bases for ease of playing. Given I have over 4,000 figures finding a set that doesn't require major rebasing or changes in unit sizes is important.
20mm ACW - still using Fire and Fury
20mm Western Gunfight - Rules with no name.
20mm Colonial - my own Zulu war rules (see Free wargames rules)
6mm WW1 - still unused - and looking for some rules
20mm WW1 - similar but thinking of modifying
20mm RCW - Red Actions from the Perfect Captain (has the flavour of the period and some nice mechanisms)
20mm Colonial/Rif - various skirmish sets, not yet settled on a single set yet.
20mm WW2 - Rapid Fire dominantly, though I do have hankerings for our old Bath Wargames Society Rules.
6mm WW2 - mostly used for solo games so my own simple rules.
20mm Vietnam - tried various rule sets, still to settle on the right one.
20mm late C20 wars/actions still working on the figs, but a variant of AK47 is the favourite so far
Ancient Naval - still using LWS rules with hexes
ACW naval - Andy Callan's rules, but using a hex cloth
WW1 Naval - still not used yet
I do use other rules, but with other peoples figures.