Hee, voting for MA/can cry in command is quite tempting!
I chose Kristy/business savvy. Seriously, she's the founder and president of the BSC and she organized a softball team. She also did countless fairs and carnivals and fundraisers and circuses and camps and all sorts of events. She's extremely business savvy for a thirteen year old and possibly an adult.
Stacey/math skills. Her math skills are exceptional. Isn't she also in a high school level math class? I know she was first in the state in that math meet book (which I hadn't read). i could see her in a college level calculus class in eighth grade!
Claudia/art. She's an amazing artist as pointed out in every book. She's won several awards and had shows at only 13. She was also in an adult art class in #101.
Jessi/ballet. She, I think, is the BSC member that'd go farthest with special talents along with Kristy.
Jessi seemed the most gifted and well rounded at the same time as well. She seemed far more dedicated to her ballet classes than the others were to their hobbies. I know dancers in real life and it takes a lot of discipline and practice in addition to innate talent. She also took to other new things very quickly (synchronized swimming, sign language, etc) while maintaining good grades and doing everything she does fairly well (unlike Mallory who struggled with horseback riding lessons).
Voted Kristy, not just for business savy but general organizer skills she demonstrates again and again in the books. Was a toss up between her and Jessi though... It is such a pity Jessi continuously states she doesn't want an actual carreer as a dancer, because I would say she was much likelier to succeed than Claud at art or Mal at writing, all such highly competitive fields. That is why I voted Kristy. Her skills could take her far.
No talent for Dawn, btw? being the most individualistic not worthy of a mention?
The other club members often called Mal a talented writer and illustrator. I have no way of knowing if she was legit good or "OMG, my friend's soooo talented" good.
As for Mallory and writing, I think she was a good writer for her age but not a child prodigy like some other BSC members were depicted as being. I've talked to people who have taught Grade Six Language Arts and they say that the stories they write are not very good compared to what professional adults write. That makes sense and I can see Mallory being like that. I think Mallory has potential to be a genuinely good writer when she grows up but she's not there yet and few eleven year olds are.