Well they're REALLY pushing the bar with Serena and Japan is LOVING the thought of Ash & Serena becoming a thing, so much so that they'll storm twitter and make "Amourshipping" a trending topic when something big revolving the two happens or if they aren't pleased with an episode revolving around the two. Even the writers have acknowledged how much the fans in Japan (Let alone international fanbase) love "SatoSere".
Worst decision he's made? I dunno. He doesn't release Pokémon THAT often. He's only released 4 while the others are still technically his but he rarely calls upon them. But even so it's not like Ash released anything special.
- Butterfree didn't do anything impressive
- Pidgeot only had 2 Gym Wins and was overshadowed by the Kanto Starters
- Lapras wasn't bad but we've seen better
- Goodra that was a dumb move. He released a Pseudo-Legendary that never lost a battle and whoop all sorts of ass in the 15 episodes he had it. Although upon reuniting with Goodra he asked if it'd help him in the Kalos League which it agreed to do so, so Ash recaptured it.
I guess not using his reserves in the League that often. With Charizard, Pikachu, Sceptile, Infernape, Snorlax, and Greninja he'd be unstoppable.