As a battling partner, I'd want Sceptile because he's just cool. Cooler than an ice cube in a Vanillish swirl. And Grass types are what I like, at least for starters.
As a pet, that's a bit harder to decide. Probably something based on a cat or dog, like an Eevee or a Meowth. Actually, can't Meowth make me money out of thin air?
Yeah, I'd like a Meowth. And when it evolves, I can sell its forehead ruby for chocolate.