H&R are 1:300 true scale, anatomically perfect, and have everything you could ask for in their enormous range.
Irregular are awful little blobs which people keep assuring me paint up well, they can obviously paint better than I can.
Adler are oversized, a little squat with exaggerated detail, this makes them much easier to paint than H&R and it is easier to identify weapons.
GHQ are similar to Adler and mix very well.
I have not seen the Baccus 20th C ranges but, based on my experience with H&M ranges, they are probably similar to Adler.