I must not be the norm. This is where my distaste of the legendary monkeys first came to pass, as I was still battling Bianca with only the non-evolved forms and figured I would outmatch her with type, but that proved difficult itself (duh), then I got a surprise critical hit against me that forced me to change my strategy mid-battle. I got down to my final two Pokémon. Not one of my proudest moments.
Cheren on the other hand came at me with all he got, but I knew he was coming after the Legend Badge and made sure I got the right team along for the trip.
So in terms of final storyline battles, I found Bianca's tougher. Given how she seems to act like a pushover, that surprised me.
Cyclone