>>281129937 (OP)
As someone who actually watched about 20 episodes of Pokemon in Japanese a couple of years ago, I can give an informed answer.
The Japanese dub is a completely different show. Not in the sense that it's better but in the sense that the characters' characterizations are significantly different. Even so, if we're comparing...
Brock is overall way way more bland in Japanese. It's only Eric Stuart in the English dub that goes out of his way to make Brock the charismatic dudebro that he is in English. No idea who voices Brock in Japanese.
As for Ash...Veronica Taylor's Ash feels more naive and childish, like a real kid unraveling the wonders of the world. Rika Matsumoto's Ash is more like a teenager mentally, Rika's Ash is more determined, has a more serious vibe to him. Both are good but in the context of the show Rika's Ash voice is more fitting I guess, but still props to Mrs Taylor.
Misty...is surprisingly good in both versions, equally feminine and emotional in her pitch. Rachel Lillis's Misty performance is the extremely RARE unique case of an English female VA properly grasping the Japanese concept of moe kawaii. Never before nor after have I ever heard an English female VA nailing the kawaii girl voice unironically like Lillis did. Like, seriously, she's the only one in the history of English dubbing who managed to pull it off.
Opening: I wanna be is kinda more catchy than the "naka naka naka" JP opening.
Ending: the Japanese ending is cooler though, the "hyakugojuu" song.
Team Rocket: I don't think there's a big difference between them in English or Japanese although the Japanese meowth sounds a bit more annoying but that's kinda the point of Meowth's "character".
Overall the Japanese dub is more adventure inspring for anime fans while the English dub is like a comfy sitcom for you and your friends. They're still the same show though.
