for me it's Julia and Shade. It was still early in the game and i trained on unsuitable mons for the fights. I've 2 mons who're practically pokedoll in those fights; 1 hit KOs
After that once i've set on my team mons, it was kinda easy (i like set ups, then use of a sweeper).
Fight with Ciel was tough though, her mons speeds are higher than mine. Making it very difficult to set up. Won due to some luck factor, which i just managed to revive my setup mons and redo the setup for a 2nd time. When i saw her final mon i just LOL, i'll definitely win her. Hahaha