There has been 8 mainline regions so far as of 2020. I honestly wanted to see your personal opinions on what your favourite region is. Whether the reason is nostalgia, Pokemon designs, storyline, game quality, memorable locations and characters, whatever, it's up to you to decide.
My personal favourite region would be Unova, as I have lots of fond memories of it, I personally don't see much wrong with the "bad Pokemon designs" either, as every region has them, and there aren't really as much of them as people make it out to be. I loved the story line and found the battle animations really immersive. You could really tell they were pushing the DS to it's limit here. Johto is probably a close second.
(Note: This persons opinions are invalid because he has never played a Sinnoh or Kalos game)
My personal favourite region would be Unova, as I have lots of fond memories of it, I personally don't see much wrong with the "bad Pokemon designs" either, as every region has them, and there aren't really as much of them as people make it out to be. I loved the story line and found the battle animations really immersive. You could really tell they were pushing the DS to it's limit here. Johto is probably a close second.
(Note: This persons opinions are invalid because he has never played a Sinnoh or Kalos game)