Right now I'm leaning against getting them(largely because I don't own a Switch) but if I did and was to buckle down and buy a version(and not both... ffs I'd rather do online trades or reluctantly do Pokémon GO to get version exclusives at the cost of saving $60), it's largely because it's Kanto. I started on Kanto and it evolves Generation 1 with new typings(Dark, Steel and Fairy don't exist in Yellow), fixes the Typing chart(Psychic no longer dominates), and adds a new follow mechanic that is not exclusive to Pikachu(not to mention riding Pokémon on land and sea to where you can visually see it in 3D).
As for what version, again this is all hypothetical but I'm leaning Pikachu Version. While my favorite Pokémon in Vulpix is on Eevee version, Pikachu itself is just a better overall Pokemon with a better Typing. Electric is better than Normal as they say when Alolan variants are apart of the equation. On Pikachu Version my team would be the following:
Pikachu(starter)
Blastoise(Mega Evolved)
Sandslash
Alolan Sandslash
Alolan Raticate
Clefable/Alolan Ninetales
Squirtle and all the Kanto starters are available prior to Brock it appears so getting a Kanto Starter early gives it a Red/Blue feel as well. I opted for Squirtle due to the fact he does extremely well against Blaine and Giovanni later on in the journey. Part of me thinks the reason we have a friendly rival is because Mr.Asshat in Gary/Blue is the Viridian Gym Leader and not Giovanni(which would be a huge twist). Anyways, getting back to my team, Sandslash is my favorite Ground Type that counters Lt. Surge, Koga and Blaine(plus Rock and Steel Types). I add in its Alolan variant because it's typing is what makes him a Swiss Army Knife. Ice/Steel is a godly combination that counters so many types that it's hard to pass on. Ice, Rock, Fairy, Ground, Grass, Flying and Dragon. What more can you ask for? Even does well against Poison due to immunity and as long as I avoid Fire, Fighting and Ground retaliation, Alolan Sandslash might be my strongest Pokémon after my run since he counters Erika(if available by then), Koga(immune), Lorelei and Lance. I added in Alolan Raticate because it's Typing makes it a pure specialist. Namely it's Dark/Normal combo makes it perfect against Ghost and Psychic Type Pokémon as it's immune to both. Due to being immune, it counters Sabrina and Agatha exceptionally well. Finally there is Clefable. A little on the slow side but makes up for it with a powerful Fairy Typing that counters Dark, Fighting and Dragon. Hence she's around to counter Bruno and Lance. If I had the means, I'd swap to Alolan Ninetales in a heartbeat and she'd be my pick for Bruno and Lance in the Elite Four.