Generally, I wish all Pok?mon (except Hypno and Mr Mime) were real. I mean, some of them kidnap (looking at you Hypno) and I'm not a fan of that, but how cool would it be to climb a tree and baam! you see a cute lil bird pokemon! or even a treecko! or to be snorkeling, and seeing all the pretty fish pokemon!! tbh I would be pretty freaked out to walk into tall grass and have a rattata pounce on me without warning but still! Otherwise:
As a pet, I would go for either an Eevee, Skitty and/or Furfrou!
As a companion in a world of battling, Incineroar and/or Greninja!
As a companion for non-battle, definitely Eevee, Pichu and Meganium.
I'd like a Pok?mon like Eevee, Togepi, Mew or Jigglypuff with the ability Pickup. But since none of them have that ability (normally), I guess I'd go for Teddiursa and hope to high heavens it doesn't evolve.
But if I were to choose, probably trubbish and garbador because they eat garbage, which earth has too much of. Just... they could kill people with the culmination of all those toxins in their body from what they've eaten, so I wouldn't want to be anywhere near them.