>>40469871I'll rank the leagues solely on whether they were actually good arcs or not.
Indigo League: 3/10
Two fully shown battles in the prelims plus two partially abridged battles. Then a 3-on-3 in the actual tournament. Rather mediocre overall. Just NPCs and Ritchie.
Johto League: 5/10
We had a preliminary battle, two 3-on-3 battles, and two 6-on-6 battles. The 3-on-3s were the strongest in this league, as Jackson and Macey incorporated type compatibility into their teams, so Ash had to follow suit. (This was also a league where Ash's Kanto starters shined the most.) The Gary battle was pretty iffy as Charizard just carried most of it, and Harrison was partially comic relief so that was meh. Charizard vs Blaziken was good though.
Hoenn League: 8/10
Probably the strongest league in terms of actual consistency. A single 1-on-1 battle, 2 double battles, and 3 full battles. The double battles were rather interesting as both characters despite being NPCs had unorthodox strategies that threw Ash off. Katie is one of the best trainers in the series as she cleverly utilizes switching and type advantages to her favor. Morrison was very iffy in the beginning but his power truly showed, and Ash nearly lost if it weren't for some bullshit from Glalie. Morrison nearly won a 6-on-4 battle effectively; his first two mons were sacked. Tyson was partially abridged and he wasn't as strategic as Katie, but Metagross was a powerful opponent.
Sinnoh League: 6/10
Two 3-on-3 battles and two full battles, not including abridged ones. Both Nando and Conway were extremely unorthodox in their battle tactics and threw Ash off in many cases, requiring Ash to improvise in the match. Ash also specifically used his Johto roster as a callback to HGSS, and Noctowl and Heracross especially shined here. The Paul battle was amazing and is top-tier in the series. Tobias is bullshit but still effective as it shows Ash's penalty for not using his A-team.