Superman has killed a bunch of prisoners in the Phantom Zone and killed Doomsday (in the same fight that Superman died). Batman just killed Darkseid.
I cannot claim any authority even on the characters I like (and DC could well have been thinking of me when they did the first Worlds Finest, because I could not care less about the rest.) Googling the topic just now turned up a bunch of comic geeks whose consensus amounts to
"Silver Age Superman never killed, but Golden Age Superman killed daily; he killed Zod with the two phantom zone minions and... well, no one, actually, because guilt for that made him swear off killing forever." With Doomsday there was no other option, dying was a fair penance and some argue Doomsday was no more than a bloodthirsty wild animal (one person compared it to Batman killing a shark.) If there is another case, okay, I will stand corrected, but it is a long way from "Superman killed once and it traumatized him so badly he never did it again" to "Superman has killed lots of times without a second thought."
Last First in wotmania Chat
Slightly better than chocolate.
Love still can't be coerced.
Please Don't Eat the Newbies!
LoL. Be well, RAFOlk.