Crusader and Artizan would be my go-to ranges to mix together, they fit seamlessly in my opinion and you can get almost everything you might need. You can find a lot of Black Tree Design WW2 second hand and a few of those blend in fine with the aforementioned.
All the others don't really fit together, Perrys are tiny, Paul Hick's sculpts are a bit thin for my liking, Chiltern are very large, Westwind (the original range) are 1/60 with small weapons, 1st Corps vary a bit, from what I have bought, because different sculptors ...the list goes on, but as you said you didn't want to get into your Old West situation again...