If Pokemon were real, I would want all of my Pokemon from my games. I would only take the Pokemon from Pearl, Soul Silver, Black, and Platinum, though, because those are the games where I truly started to get emotionally attached to my Pokemon instead of just playing through the games. Some of them are duplicates, so I would just take the one I had first (when I have duplicate Pokemon in two different games, I just consider them the same one on a different cartridge).
I'd definitely have a diverse group of Pokemon, but it would definitely be useful. I'd have Empoleon, Luxray, Meganium, Ampharos, Togetic, Samurott, Victini, Lopunny, Altaria, Girafarig, and Rapidash.
I don't know if I would battle regularly, but I'd probably do the gyms. I don't think I would go for the Elite Four, to be honest. In real life, I'd be too afraid. I would spend most of my time just playing around with my Pokemon.