Not Talking about the games. Strictly the regions themselves.
Sinnoh
Hoenn
Jhoto
Kanto
Unova
Alola
Galar
Honestly I probably would say this is super close. Sinnoh and Hoenn have such dope ass biomes. Unova a sleeper lowkey but it’s hard to put it above Johto or Kanto
Johto > Hoenn > Kanto > Sinnoh > the rest
in terms of design and exploration
hoenn
sinnoh
johto
alola in usum (don’t know if there’s a big difference, haven’t played the original)
kanto
galar
unova in bw2
kalos
unova in bw1
unova in bw1 is legit designed like trash and built around a garbage story
i used to love the bw games but as time goes on i just don’t like em
they look ugly, the unova region is boring, the pokemon are ugly, the forced story sucks
just a mess all around