All of the Fleischer "Superman" shorts are magnificent, as far as I'm concerned.
At least from the standpoint of hand-drawn animation, they've never
been bettered. Certainly, they're close to the same level as a lot of the shorts and features that Walt Disney was doing at the same time. The rotoscoping (which recreates human movements) is terrific, the character designs spot on, and the visuals are spectacular. Additionally, I always loved how -- and this is so representative of the era -- some of the best aspects of 1940's "film noir" are employed, such as when Clark Kent transforms into Superman, and you never see anything aside from a silhouette behind a pebble glass store room door, phone booth, or his exaggerated shadow thrown upon a wall or some other surface. It's almost never out in the open. Along with Sammy Timberg's music score, it always makes it fairly dramatic.
I'd actually go as far as to say that it's too bad there were only seventeen episodes, and that the Fleischers couldn't manage to do a full-length feature at Paramount along the lines of "Gulliver's Travels." The cost just might have been too prohibitive.
A part of me also wishes that someone would do a cartoon series set in this 1940's WWII-era period -- Rob Pratt's short, "Superman Classic," probably comes closest:
As for the Fleischer shorts, my favorite episodes would have to be "Billion Dollar Limited," "Electric Earthquake" "The Magnetic Telescope" and "The Mechanical Monsters."