The only other American sci-fi strip with top-notch artwork that I'm aware of off-hand was Twin Earths (1952-1963), created by publications maestro Oskar Lebeck (1903-1966), who did the writing in the early years and Alden McWilliams (1916-1993), who did the art. I will probably write more about McWilliams in another post, but shall focus on Twin Earths here.
The concept of Twin Earths was that there existed a totally Earth-like planet that shared Earth's orbit but at exactly the opposite side -- 180 degrees away. This meant that, as of 1952 when the strip started, there was no way we on Earth could detect Terra, as it was called. Terrans were a few hundred years ahead of Earth technologically, so could visit here using their flying saucer spacecraft. Another quirk was that their population was 90 percent female. Yet another was that they had lifespans exceeding 150 years, yet preserved youthful appearances over most of that time.
The opening few months of panels can be found here. A Terran female agent reveals her identity to an FBI agent, the male hero of the strip. Then things flow from there.
The Seattle Times newspaper suffered a strike in 1953, and when it ended the paper published special sections displaying all the comics that would have been printed during the time of the strike. I recently made scans of these for Twin Earths, and two of these are displayed below. At this point in the strip's development, the plotting wasn't very interesting. Mostly it was presenting the futuristic marvels of Terra, contrasting them with 1953 Earth. There was a bit of romance-related activity, but no space wars or bug-eyed monsters.
I'll comment further in the captions, but want to stress McWilliams' artwork. Grinding out comics panels day after day can make corner-cutting tempting. Yet McWilliams didn't seem to fall into that mode very often, maintaining a commendably even strain.
Click on the images to enlarge.