>>54295434BW Ash is a regression in terms of skills and temperament. It's like they reset him to his rookie days.
SM Ash is actually stupid and childish in a way that he wasn't before.
>>54295705Part of it is I like May. She has a very fun personality; she is dumb, but not actively harmful. Her arc is also really well done. She starts out disinterested in Pokemon, ignorant of why people like them and seems only interested in being able to travel. But over the course of the series, she gets involved in Contests, grows to love her Pokemon, even becomes competent in battling. Max as a fourth member helps round out the party's dynamic in a way that other groups don't necessarily. Related to that reason is that I like the concept of Contests a lot. They allow for unpredictability, since May doesn't have to win all of them. The rivals for the Contests are also great. The other part is that AG's filler is really great, and makes for a good in-between from Ash's Gyms and May's Contests.
While May's my favorite, I also think Lillie, Mallow, Lana and Dawn get a leg up on her, just from the strength of their arcs. Misty is next. Then Iris and Serena are probably equal, although Iris does eventually become champion. I don't know about Koharu yet.
Serena's weakness is that her arc is very similar to May's (start from zero, find a goal, pursue it and become passionate about it) but it's slower, there's less of it, and it is weighed down by shipping that they were never going to deliver on. When she's not in the focus, she tends to disappear behind Clemont and Bonnie, who fill the Brock/Max role of XY. I don't think any of the other companions aside from maybe Tracey have that problem as consistently.