That pic of Jubilee was from a deleted X-Men 2 scene.
Anyway, Kitty's been around a lot longer, and has more skills to her name past her powers. She's a ninja, a hacker, extremely smart, with gymnastics and dance training that can be used in combat, and a pet miniature dragon. That said, she accumulated all these things over years of development, and is in fact has had one of the longest and most developed character arcs in all of comic books.
It's also got to be taken into account that Jubilee's been held in a kind of character stasis since the mid-90s or so. Regardless of what changes around her, she herself doesn't change on a fundamental level.
But she has a lot of potential to be an interesting, fun character. She just needs to be allowed to grow past the bad fashion trends of the 90s and into her own.
Also, I miss her powers. I actually liked the visuals of her "fireworks", and the fact that she can control them with her mind once they're released from her hands. That's pretty rare for an energy-wielder. And she's potentially powerful, too...in one of her earliest appearances, she blew an entire wing off a Chinese palace when she thought Wolverine had died.
So even though I prefer Kitty for how much she's grown, I still like Jubilee for who she could be.
Sprite! Her introduction to the title was just so awesome.
I honestly like Jubilee a whole lot back in the 90s when all I knew was the SatAM cartoon. Then I started actually reading the comics. Now, Jubilee just kinda feels like a character they introduced to replace Kitty as wolverine's creeply young girl sidekick (seriously, why do they do that?) who has since been replaced in that role.
Also, Kitty has a pet dragon. QED.
Powers wise and Knowledgeably speaking, I would choose Shadowcat for the reason of her being so much more skillful than Jubilee.
But if I have to say Leadership wise, then maybe Jubilee qualifies because she has a lot more experience as a mutant that Shadowcat, I am basing this to the X-Men: Animated Series wherein she's one of the first youngest leaders of X-men.
I just hate the fact that she wasn't even really introduced as Jubilee in the movies. I am really upset with this...