Best Wishes (unironically) started off very, very promising. I can honestly say I was really excited about most of the new characters and the plot that was being build-up (yes, I could even see Trip ending up somewhat as a decent booksmart rival compared to Ash's improv-style). And then the 2011 seaquake, tsunami and Fukushima meltdown happened and a lot of that what was planned supposedly got binned and never seen of again. Then they rushed the entire region to get to the League, leaving barely any episodes for development of the pokemon and/or human characters. I distinctly recall Castelia -> Nimbasa taking forever (edit: 6 months) and the last 3 to 4 gyms being done in what seemed like 2 months (edit: gym 5-8 was the stretch 61 - 83/84 and took the same amount of time as getting to Nimbasa from the 3rd gym). I mean coming after Sinnoh, which did amazing with the Paul/Infernape-storyline and well enough with developing other Pokemon, you couldn't help but assume everything just got chucked and we didn't get the real planned effort. I mean Ash had a massive line-up and instead of seeing those pokemon get developed going towards the league, we barely got to see them at all and if we did it was during a battle. Just a hint: Snivy, a starter of all things considered, didn't get ANY new moves or worthwhile development. It was just there for promotional purposes and one literally never appeared outside of battles.. Again, compared to Sinnoh where the stretches between gyms took about 15 episodes on average, there was the necessary time to breathe and develop rivalries and pokemon. Heck, we especially saw Ash work on his pokemon during the Snowpoint -> Sunyshore gap so we knew they were being made ready for the league instead of being phoned at the end.
Iris was a highlight for me with each of her character-episodes giving a nod to her becoming closer to her goal (even if some disliked some writer choices). Cilan was pretty mèh to me, but he had his fanbase.
After the league (which you heard about) we got a decent adaption of the N-storyline. And then we got the Decolore Archipelago-arc. Which added a string of unnecessary fillers which could've been better used to space out that ep61-83 rushfest and give Ash's Pokemon more character development.
So I'd recommend watching all episodes until the Castelia-arc, then the DonTournaments-arcs, GymBattles and Iris episodes. Actually, I'd just recommend watching most episodes up to the league as it's not as bad as many people make it out to be. Just skip what are obvious fillers and you can condense it to about 50-60 episodes or so 70 at most.