Eh, I’m not so sure. Nightwing and Tim Drake would give him a run for his money.
I’m surprised no-one’s given any thought to whether the rest of the Justice League could whup him.
Without prep pretty much anyone of them could beat him.
On the Marvel side I’d add Spiderman, Captain America, Iron Fist, Black Panther, and pretty much every other Avenger accept for Hawkeye.
Together or individually?
Dick, maybe, but not Tim. Tim’s pretty much the worst fighter of the currently able-bodied members/former members of the extended Batfamily. (With the likely exception of the new Batwoman)
He’s less experienced than just about any of the others (except Batwoman), less focussed on the combat side of things (MAYBE except Batwoman) - he’s a detective in training, not a fighter - and, unlike Dick, didn’t have a background he could adapt for it.
I dunno . . . ya gotta take into account that Robin is younger, and remember who he studied under.
Point taken, Tengu.
Out of the rest of the Bat-people, I think Cass could probably take him.
Depends on the kind of contest, of course. Batman has always relied on his wits more than anything else – he might have an advantage in any kind of intellectual contest. I wouldn’t give Green Arrow or Wonder Woman any odds against Batman in a chess match, even if Batman hadn’t played chess since he was 12.
Dr. Fate or the Phantom Stranger, OTOH . . . there’s really no telling.
And Alfred?
The answer to the OP, though, is, I think, anyone (regardless of membership in the Justice League). Even Bruce Wayne has to sleep sometime, and if he’s not prepared, I think it’s plausible to suppose someone sneaking up and smothering him with a pillow.
Justice League, anyone?
Ah, so that’s what JLA stands for!
Lex Luthor and Swamp Thing are two significant DC Universe characters who HAVE beaten Batman.
What, no love for the rest of the comic book world? I think the feat could be accomplished by almost anyone with actual super powers, like the rest of the Justice League, for instance.
That’s because Swamp Thing doesn’t need to be prepared. Just rinse and serve.
I was thinking the costumed members…Tim could take the current version of Alfred in a throwdown. Although Alfred is a fairly respectable fighter, just not on the same level as the actual heroes.
Done, in a crossover; they came out even.
Anyone with unavoidable powers, like Professor X, could beat him easy. So can anyone with powers/weapons capable of widespread destruction. Dr Doom nuking Gotham comes to mind.
The origin of Cajun cuisine! 
The Forgotten Heroes, perhaps? Or maybe the Inferior Five?
Awkwardman could take an unprepared Batman!
The Blimp could hover over him in his sleep, then crash down and smother him, like Chronos said.
I’m likin’ the idea of a Plastic-Man-versus-Unprepared-Batman matchup. Any ideas on how it might go? And can Woozy Winks take on Robin?