Ugh. Yes, we get it, they're for kids. But not all of them are "cringey" or whatever. =/ Pokémon is for kids, we get it. That doesn't make adult's opinions of the theme songs invalid.
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Anyway, in my opinion, every series, except Unova, had really earwormy, catchy theme songs. But Hoenn and Kalos honestly had the best mix. Sinnoh had some interesting ones that got completely stuck in my head as a kid, but some were kind of lackluster.
Kanto's is iconic! The Japanese one is kind of weird, but "Pokémon, getto daze" always got to me...