I haven't seen it yet, but from all the raving reviews I'm looking very much forward to watching it. I see every Marvel and DC movie. Hell, I'm a sucker for any kind of superhero movies, but X-men in particular.
Sadly I've not been to the theaters in a year now or so because I've been to lazy, so I'm guessing I won't see Logan either before it hits Xbox One store so I can rent it (probably 6+ months from now).
About x23. It's really a kid phenomena. I remember a very famous actor (dunno who, it was like 15+ years ago but one of the biggest back then) once say something along the lines of: "Never act against cute animals or small kids. They'll outperform you every time".
What he probably meant is that the cuteness factor and kid factor counts manyfold when we watch young kids perform something, especially if their parts are just a little bit cool (Think Mathilda from Léon, Hit-Girl from Kick-Ass, Cole from Sixth Sense and now also X23 from Logan - and there are probably more)
It just adds something in our minds. Same goes for kids in horror movies (think about almost any Japanese or Korean horror movie - always kids and it's scary as fuck).
It comes from several reasons - one is the coolness factor of seeing a little kid going crazy on people (in real life Hit-Girl would not be able to tossle around with any grown man - physics of the weight difference is just too big etc) - but it's also that we are a lot more lenient towards what they do. We don't expect much from kids - or we don't really pay much attention to how the really perform and they have a lot less focus on them and pressure when doing the movies so they can focus on just having fun.
This all goes away as they grow up of course - and we're seeing it with Chloë now. She's living through the problems
of being a teen and now young adult actress. Natalie Portmann handled herself rather well though never as superior as Matilda. Haley from the Sixth Sense - well he fucked up and fell into the Hollywood kid trap and never became the same. I saw him as one of the biggest upcoming stars back then, now I don't even know him).
Ah, late rambles. As to your question about a fight between X23 and Hit-Girl. I haven't seen the movie and I don't know much about x23. Her being a mutant with regen powers does give her a clear advantage vs a normal girl who can get hurt. I'd say that alone would win the battle. She doesn't have the ademantium in her body (only her claws as I remember), but still, regen wins.