Harley isn't serious enough to win. She'd probably crack a joke while she's getting the spades kicked out of her.

I actually just remmebered that she didn't win in the book because she got shot in the sholder by Harley.

Already proved in Hush.

Harley's instability would be an advantage, but Selina's skill would give her the ultimate edge.

Selina but its not really fair.. selina has fought people in the likes of.. basically anybody in the DC universe and harley is quite good but shes still learning.. not to mention selina was trained by two of batmans masters soo.. there ya go

Harley... Here is why... Selina is wiley, crafty, and skilled in fighting of course. But she's also simply a glorified gold digger in a costume. Harley is wiley, very crafty, but the most important... That chick is crazy as hell! She's psycho! She lives with the JOKER for goodness sake! It's sort of like putting Steven Segal or Jet Li against a guy with a machine gun. And I can guarantee you, Harley has the Machine gun...

Harley Quinn for the win!

Selina's a bit older, has a good deal more experience and has a better head on her shoulders. Harley would play dirty but Selina would come out on top in the end.

As you well know I love me some Harley...BUT Selina would kick her ass from here to the kitty litter factory (which you know would somehow get involved) At first I thought Harley cause Mr. J's got her back but then I realized that given the nature of their fucked up relationship that might not actually be a plus. So, after much considerations...Selina FTW.