Hello, think about to buy 6mm Vehicles. Not GHQ(to expensive) and Irregular (to ugly).
GHQ is expensive but worth it. Especially for those "halo" units or models. BUT the infantry and especially horses (draft) are a pain. The infantry is delicate and draft horse usually don't have bases which makes them a major pain. I replace GHQ draft horses with H&R ones.
CinC is available from LegionsIVhire now. Almost as good as GHQ. But the detail is not oversized like on GHQ. So a thinner paint is a benefit. Not the range of GHQ but still very extensive.
H&R is my go to for both items not done elsewhere and infantry and cavalry. Also since the new guy (can't remember his name off hand) has taken over he is introducing new and interesting lines (lots of WWII Airborne from both sides) and has been having many older models redone so they are as good as GHQ maybe 10 years ago. Plus he has brought back many (all?) of the non modern/WWII lines so the range of items is matched by no one.
Baccus is getting their masters done by 3D printing. This makes for really good originals (close to GHQ). Having seen some they do look a little large(ish). Still filling out ranges.
Scotia Grendel. I like them. Yes low detail but last year I finally painted my 40+ year old stash of WWII French. Must have been something like 30 models of vehicles and guns. And still more and the new ones are as good as the H&R. Who makes Polish Belgian and some 45 French WWII models?
Irregular. Yes the vehicles are pretty sad but I really like the infantry and cavalry. Imaginative poses and if you can live with the already based design then wonderful. Almost as extensive as H&R and an even wider lot of ranges. I have a ton on Spanish Civil War figures for use as any sort of troops from interwar to post war irregulars of colonial troops plus imaginations.
There is some new outfit out there who does very specialty models. Like recovery vehicles and what if WWII in '46 or '47. Can't for the life of me find them in my badly organized (unorganized) links but worth a search. I believe they also use 3D printed masters.
Lastly Skytex(?) and Croissant (in service miniatures) and a few others were from days gone by. Very variable but I like the ISM range. He added things like sand bags, logs and stowage to existing vehicles for the lived in look. He also did really odd ball stuff like tractor-trailer rigs, telephone poles, earth moving equipment, etc.. Not common but can still be found (at least in my basement).
If you want modern or aircraft then this will get really long. Let me know if you do as I have many from WWI to ultra modern and into sci fi. There are quite a few sci fi 6mm producers out there with many figures suitable for irregulars or what ifs. I have some figures to use as African rebels and South African irregulars.