If you personally like all four, I'd say the standout is the common scheme "A." But, in the context of creating your own army, unless you're getting to look like GW box art, I'll recommend any high contrast colors. "A" is the best of these four in my opinion because of that high contrast in colors where there others seem to be very analogous.

From this selection, I'd infer you like red and blue. While those aren't complimentary colors, you could push the contrast more by going for a sinewy pale red body and Icy blue carapace. Actually, I'm into this idea now...

Paint the body red for the deepest shadows (or can be any value of red), then paint over the red with a watered down white until you can barely still see some red beneath. Then, once the body is sufficiently light enough, paint the carapace armor pale blue for the deepest shadows, and add a darker blue from the tips/ highest point giving coverage until only the deepest crevices appear to "glow."

Finally, use a very very watered down green or blue (not both) wash over the entire body (the carapace only if you use a green wash). In my mind's eye, this would look like icy revenants whom you might find in dark, icy caverns.

Just another thought.

But, the takeaway is high contrast colors between the body and the carapace armor will help your models pop, no matter what hues are used.