Hoenn Elite Four in Emerald. There are plenty of Grass and Electric-types, which takes care of Wallace, and other than Drake the other's aren't especially menacing except perhaps Walrein. Phoebe's Ghost-types do drain your pp incredibly though - I'm thankful for the invention of the Leppa Berry.
Unova's weren't anything special, but they weren't weak. They were all stronger than Aaron from Sinnoh, anyway. I do think the original Kanto Elite Four may be one of the hardest, from my experiences in LeafGreen.