Those are great, I especially like the six-gun western. My sense with Maneely is that for each cover like those above, there are 3 or 4 others that are relatively bland. If you contrast that to Heath or Everett, the ratio is more in favor of great covers. At least in my opinion.
That probably reflects my affinity toward covers with a little action as Maneely tended to draw static poses and situations. As you've said, you prefer those which I would imagine explains your fondness for Maneely. I think as a technical artist, and stylistically (linework, not layout) as well he is up there with the best of them. But I prefer the content of other artists as a whole.
Don't get me wrong, I like Maneely and think he did some wonderful work, but looking through my war books his action scenes were often lacking (in fact the two covers of his I really like are more static - Battlefront 11, War Action 12). Maybe the editor(s) at Atlas recognized this and put him more on the Western line where he could put some tense "stand-off" images together; more in line with the content.
I'm just making this up as I go, so please no-one take this as gospel.
Here are the two covers I referenced.