Grab Batman, lift him up to 250nm AGL and let go.
Fight's over.
I had similar ideas.
-wait til he sleeps, drop a mile-wide boulder on him
-throw him into the sun (or drop him off on Jupiter)
-bring him to the bottom of the ocean for ten minutes or an hour
-eye laser him to shreds from a mile up
-grab his batmobile as he's driving it, flip it upside down, smash it with your super feet until it's flat
-fly by at 450 knots, grab an arm on the way by, rip it off his body; repeat
-fly straight down, fist out, fast as you can, and pummel him into the earth about 10 miles down
-grab him, before he can act, super-squeeze the guts out of his body
Why there was any kind of "fight" means superman wasn't really trying to kill the bat.
I'd be way more of a jerk than superman is. From the trailer, batman asks if superman bleeds, and follows up with "you will"... I'd punch him so hard his lungs came out the other side of his chest. Then I'd ask "...you were saying what again...? I feel like it's apology time, don't you? ...or are you happier with your head traveling about a mile that way?"
Like I said, I would not be a noble superman with batman all being dicky and everything.