This isn't a comic that is actually in the shortbox (there I go, breaking my own rules already). It is, however, the first specific comic that I have a memory of.
I can remember being given comic books, along with my cousins, to keep me busy while the family was keeping vigil, waiting for my grandmother to die; that must have been when I was about six or so. This comic is from a few years later, in late 1966 or 1967 (the book is dated March 1967). While it is not the first comic I ever read, for some reason the cover image has stayed with me all these years; when I found an image just a week or so ago, I was amazed at how accurate my memory had been.
Let's leave aside all the wonderful siver age goofiness: the DC go-go checks, the crowns on the heroes (Superman sorta looks like Jughead, doesn't he?), the yellow-oval batsuit, and so on, and look at just two things that made this cover memorable for me.
The first element that appeals to me about this cover is the use of the dramatic gesture of slicing the globe. These guys are dividing up the world between them, and they're not just making lists or drawing lines on maps: they are slicing up a globe with swords. I think that gets a real multi-layered point across about power and greed and force; it did to me when I was a kid. I remember just studying this cover and all it had to say.
The other thing that I have never forgotten about this cover is that it is where I learned the idiom "lion's share." I was an avid reader as a child - not just comics, but all kinds of "real" books - and I have to say I learned as much from silver age comics as I did from any other source of entertainment reading. It wasn't just the PSAs and the Science Says You're Wrong features presenting unusual facts; it was the subtly sophisticated language of the stories themsleves, the allusions to historical and literary figures, the use of real science and law in plots. Later, I figured that this content must have been the result of the comics' being written by people who actually had had full lives and experiences outside of comics, and who brought to them a complex sensibility. (I can remember how astonished I was when I learned that Gardner Fox had been a lawyer.)
Anyway, that's where I am coming from: I'm a guy whose comics taste may have been determined by thinking for 39 years that the cover of World's Finest 165 is great. We'll see how far that takes us.