Depends on the book…
WoK: Definitely Kaladin, he was better the whole book but that scene where he lands and speaks the 1st ideal is carved into my brain.
WoR: Shallan without Jasnah gets a chance to shine, and Kaladin takes a back seat more as we learn more about Bridge 4
Oathb: Shallan really came alive in this book and is as engaging a female character as Ive ever read.
RoW: The Lopen lol. Joking of course but Id put Kaladin ahead of Shallan in this one mostly because Shallans mental health issues reminded me too much of her slow (not bad just slow) start and meeting Kals family gives a great backdrop for his development.