I read these all the time when I was a kid, and to me they are perfect examples of SF cover art.
You can't go wrong with an axe and lots of red hair, right?
This one is just so goofy. I love weirdo covers like these.
I love these because they're so perfectly typical of the period's style, so surreal and supposed to be all symbolic.
My husband also likes SF art, and his tastes run to John Berkey, Vincent di Fate, and Chris Foss -- spacescapes with huge ships or structures hanging in front of planets. Whenever I read Archer's Goon, Howard and his spaceships reminds me of him. Here's one for the husband, "a really complicated spaceship, full of unnecessary but soothing twiddles."