I guess Houen's Saiyuu Tournament, for the reasons Gravy also mentioned. I mean, looking past the horrid rush-job at the end.... it's f*ckin' Kaede, man. What's not to like? There's also the fact that Masamune was Satoshi's most likeable main rival to date, and we got to see several of his battles beforehand. Nyaasu-in-boots was also pretty interesting.
Kantou ended on a very sucky note, Lizardon just falling asleep (I once again state, though, the Dengeki Pikachu version kicked all kinds of ass. Lizardon still costs Satoshi the league, but it's because it had to be recall after mercilessly attacking Hiroshi's Lizardon). Whirl Islands.... that entire mini-arc sucked. I too liked Satoshi's Orange Island team, and that was a pretty sweet battle, but I agree with what was said about it being just a single battle in the end. Grand Festival was good, but aside from the appeals round, all we really saw in their entirety were the battles against Harley and Shuu. Haruka vs. Tonpei and Shuu vs. Robert, we only caught the end, and all this was in a single episode, being shared with Satoshi's sideplot.
Jouto did resolve Satoshi's rivalry with Shigeru, but like Houen, it suffered to rushing problems in the last two matches (well.... maybe one-and-a-half. The first part of Shigeru's battle was good), and Jun'ichi and Moe aren't quite as likeable as Satoshi's opponents (and Tetsuya and Masamune's opponents, for that matter) in Saiyuu. I also think it sucked that this was basically a way for the Kantou starters to whore all the spotlight for the nth time (especially Zenigame, who seems to come in from supposedly nowhere immediately after Kingler's so conveniently taken out of the action).