The hardest (for me) was Shauntal (both before and after main-game), then Marshal, then Caitlin, and the easiest was Grimsley since I had Emboar. Just having a decent Fighting Pokemon would easily take care of Grimsley and Caitlin was very easy as well when you have an Umbreon (post game) pre-game was actually harder cause I didn't have an Umbreon at the time and I fought against her with a Configus (whatever the crazy looking Coffin Ghost Pokemon is that evolves from Yamask). Marshal was easy, but tougher than Caitlin cause I had 2 Psychic Pokemon (a Siphith and a w/e Woobat's evolve form is), but I got tired of all the Sturdy abilities, and Shauntal was a big challenge and nearly lost to her. Since Ghost is strong against Psychic and Ghost, I lost Siphith, Woobat, and Configus. Emboar was able to do a critical hit against her Configus with a fire attack and I traded for a Simipour so it took care of Chanderler. My Pokemon were Woobat, Siphith, Emboar, Simipour Configus, and Vaniluxe, and only Emboar and Simipour remained after defeating them.