When was the last time Buffy fought ALONE? The whole "it’s a secret identity" thing limits both Batman and Superman. Either of them might be able to take out Buffy, alone, but I don’t like the chances of Batman and Superman combined against Buffy, Willow, Faith, and Angel.
Batman has taken down many individuals with superior strength, His martial arts skills have been taken to nearly supernatural
levels in recent years. Of course Buffy’s strength is supernatural so for the sake of argument let’s say that Buffy wins the first
Round...After which Batman goes into "Research Mode" maybe employing Oracle(Barbara Gordon,DC’s resident information broker supreme) to uncover the Watcher’s records (If the robot ninjas of Angel’s fifth season can Oracle certainly do the same"
Including, of course the "Cruciamentum" formula used by the Watcher’s to neutralize a slayer’s power for testing purposes.
Creating a weaponized gas form of the same Batman takes the human Slayer down...Later naturally they team up to take down a common enemy lol...
Batman would win, Buffy doesn’t stand a chance. If Buffy enlisted the aid of the Scoobies and Angel Investigations she would still lose because Batman would bring in the JLA. I agree though these things are silly.
It’s a lot tougher battle than most of you would think.
Yes, the Bat was able to beat Superman. But then Superman has a major weakness that Batman, can use to his advantage - called Krytonite. Buffy doesn’t have such a weakness. Yes, Batman’s smarter and has lots really cool toys. But, Buffy has the advantage of superhuman strength, and agility. Yes, the Bat has some major foes(all of whom are basically human). Buffy faces powerful superhuman foes on regular basis.
Buffy may have a few surprises for the Bat, in the fact, that he likely would think such a small girl could be so strong and fast.
And as for Buffy, Angel, Faith & Willow vs. Superman & Batman. Here’s how I see it. Willow immobilizes Superman(remember that magic is his other weakness), then Buffy, Faith, & Angel take out the Bat.