"World's Worst" from World's Finest Comics #156 (DC, 1966) by Edmond Hamilton, Curt Swan and George Klein
My era of World's Finest Comics was the tail end, in the 80s, obviously, when Superman and Batman were good friends whose friendship had recently been tested. It felt natural, and it would take years in the post-Crisis era before they could be that friendly again (if they actually did, I'm not sure). But the stories weren't particularly memorable. I've since gone back to discover older, crazier stories from the Silver Age (above), and the Super-Sons stuff from the 70s, and obviously, the book dates back to the Golden Age where it presented other strips like Stat-Spangled Kid and Green Arrow (and would again, Clark and Bruce weren't always the world's finest team in the Bronze Age). I don't think these ever WERE the World's Finest Comics, but you could argue that at least, Superman and Batman were the World's Finest TEAM. For a while at least.