Obviously, Ditto is the most handy, in the manga canon you can use it to appear like any person by putting it on your face. Brilliant disguise and any Pokémon at your disposal.
Other than that, Flygon is tempting, aesthetic-wise, it's a beautiful Pokémon, IMO. They aren't huge, only 6'07''. Summoning sandstorms would be a great party trick for getting rid of troublesome people. She could all char-grill passers by with dragon-type moves or wipe up a heat wave (har har). I can see myself with a harness on one travelling in the sky. And it's one of my favourates.
Another choice would be Roserade, I have this image of it using Grass Knot to entangle people too close to me, and laying down Toxic Spikes. Not to mention, how portable it is.
Or perhaps Militic. I love swimming, and it would be a fun Pokémon to take on a beach holiday. Or Slowking. It's just their cute little faces...
I wouldn't want a Pokémon that resembles a real-world animal, I'd love something wacky, out there.