For me, it's Kanto. The best Pokémon region. I even ask for extra Kanto and Game Freak is so friendly and more than willing to oblige.

One time I asked for Kanto and they gave me remakes in gen 3. I said, "Wow, gen 3 for free!" and the nice friendly Junichi Masuda laughed and said, "I'm going to call you gen-3-for-free!".

Now the staff greets me with "hey it's gen-3-for-free!" and ALWAYS give me more Kanto. It's such a fun and cool atmosphere in Kanto, I go there at least 3 times a week on my Game Boy Advance, 1-2 times on my Nintendo Switch on the weekend, and maybe once on my phone emulator when I'm in a rush but want a great Kanto experience that is affordable, fast, and can match my daily nostalgia needs.

I even see Kanto in other games, it's fantastic! What a great company.