I am a huge fan of GHQ products. I just love the quality of the mastering and the molding.
That said, I also have a large quantity of other vendors in my collection.
In most cases if a model I want is available from GHQ, that will almost always win my purchase. If not, C-in-C is almost as good. If not, then H&R is my next choice. I have bought a lot of H&R over the years. I am particularly impressed by the new models coming from H&R. Bravo to the new H&R crew! I also have some Scotia product. I like some of the off-mainstream stuff they do. But honestly, between H&R's older stuff and Scotia I really want to see a picture of the model before I buy, because there were a few that I did buy that really were just not quite good enough for me.
I gave up on Skytrex 1/300 more than 20 years ago. So much of what I bought wound up in the "lead by the pound" bag. But the pictures I've seen of their more recent stuff seems much better, so perhaps I should give them another try.
The Irregular stuff
I think I'll pass. Sorry, but from what I've seen they just don't do it for me.
In my collection I mix the manufacturers without hesitation. OK
I very seldom mix the same model from different makers, but different models in the same unit work just fine for me!
As examples:
Here is a Romanian armored car team
some kit supplied by their German allies (GHQ's SdKfz 222s) and some kit captured from their Russian adversaries (some H&R BA-64s). They mix just fine for my purposes.
Again from my Romanians, we see a battery of C-in-C AT guns (Pak97/38)with H&R gun crews (Soviet figures standing in as Romanians), GHQ prime movers (SdKfz6's and Lafflies), protected by a security squad of GHQ infantry (Romanian individual infantry).
Here is a picture from a game in progress. A GHQ Italian L3 light tank leading a GHQ Lancia truck full of infantry comes face-to-face with an H&R French AMD-178 armored car in a village in the French Alps.
Yep, I mix vendors in my forces, in my units, and even on the same stand (with the infantry) without too much hesitation.
I've never had anyone tell me they didn't want to game with my models because of the mix of vendors.