I think having a jolteon living outside his ball would result in a lot less pokemon being caught, for this reason: have you ever tried getting rid of something with a dog that loves to fetch?
Also, I think if they got too excited, they'd shock people. They'd be very painful pets--can you imagine coming home from work with this guy waiting for you? "Hey jolt! It's good to be homeeeahhhghhh!" That's not to say I still wouldn't get one...
I picture him as a sort of terrier-mutt type of canine. Probably because wire-hair terriers look like they've been electrocuted anyway--it's adorable.
Incidentally, my other favorites were ninetails (by FAR), arcanine, rapidash, the other eeveelutions (I've since learned that's what the other forms eevee turns into are called), aannnd...I think that's it. Nothing else comes to mind at the moment, anyway.