Red

Thanks All. It seems Soul Silver/Heart Gold is a good idea, remake of a classic game, so I can still sense what its all about but with better graphics. It seems Black/White is also very well regarded, more or less from the same era as Soul Silver/Heart Gold with similar graphics. I guess I will choose one of these.

I actually only played one Pokemon game until this very day, which was Pokemon Yellow all the way back in 2000. I have zero regrets, so I will recommend that one.

Good choice, SS/HH have all the core improvements of 4th gen that have formed the core of Pokemon since but are also rich in content and character themselves, probably the most complete in the series.

Pokémon Emerald is the game you should play. HearGold/SoulSilver are great games, but they are sequels to FireRed/LeafGreen. Not that they are super connected, but still, you would enjoy HeartGold/SoulSilver more if you had played FireRed/LeafGreen before

Pokémon Emerald is the game you should play. It has a great map, the exploration is awsome and the Pokémon roster is great. It also have a more structured story that any of the old pokémon games, except Black/White. HearGold/SoulSilver are great games, but they are sequels to FireRed/LeafGreen. Not that they are super connected, but still, you would enjoy HeartGold/SoulSilver a lot more if you had played FireRed/LeafGreen before

I owned Pokemon Blue and absolutely loved it back in the day on the OG Gameboy in 1996. (And upgraded to the Gameboy Pocket that same year, much better display.)

....And then I never touched a Pokemon game until Pokemon Sword/Shield on the Switch.

And the TLDR is... I felt like I was just playing a rehash of the original Pokemon Blue game from several decades prior.
The tropes, the mechanics and so on hadn't really progressed... Sure it looked prettier, but look beneath the surface? Same game.
Originally I thought it might have just been Sword and Shield playing homage to the original titles... I could even guess how the story would unfold before it happened, almost like I wrote it.

So I started hunting down other games like Pokemon Ultra Sun/Ultra Moon on 3DS and Pokemon Black/White on DS...

And the result? They are Pokemon games. If you played one, you have essentially played them all... If you are expecting a massively complex, invigorating story with unique characters that have personality between the different releases... Then you might be disappointed.

That doesn't make them bad by any means, it clearly appeals to some, but it does mean that there really isn't any reason to play more than a couple of games in the franchise unless collecting Pokemon (which is playing on peoples addiction) and transferring them around is your thing. - It's just not mine.

For phone emulation I would probably jump into one of the GBA games like Emerald, it's light, easy, has visually aged well and Emerald was probably the definitive GBA release.

Personally for introduction i'd choose Pokemon Yellow for classic (Pikachu follows you!) and Pokemon Let's Go Pikachu/Eevee for modern.

If you own a Switch 2 I would pick up Pokémon Scarlet or Pokémon Violet i have heard a lot of good things about these two games.

100% Black or White.

They’re the best story wise, you can get all the Pokemon, it has a direct sequel if you love it. Seriously. Gen 5 is where it’s at.

Heartgold/Soulsilver are of course great options too, and Emerald is wonderful if you have a GBA.