Most: Espeon
By the time I evolve Eevee, it would be very obedient as a result of sufficient training and TLC.
It would be really loyal to me, and as a Psychic-type, it can easily sense what's wrong, allowing me to take action if needed. If it's chill, all is well and it will save me more unnecessary stress.
Cute Pokémon put a smile on others' faces, and considering that Eeveelutions are ridiculously, but reasonably popular, I will have great internal and external support.
Least: Charizard
Charizard may be one of my favourite Kanto Pokémon, but it would be a terrible roommate.
Not only is it known to be rather disobedient and lazy, but it will incinerate all my rare and expensive belongings with it's Fire-type moves, regardless of intent.
It may be an awesome fighter, with or without Mega Evolution, but living with one is hell.