Misdreavus It would affect my daily life by...being my favorite Pokemon. This would be awesome! I'm fairly certain people would notice a disembodied head floating around me, yes. Misdreavus would help me...I dunno, pull pranks on people?
My favorite pokemon is Umbreon, but I don't think he would be all that difficult to deal with, really.
I would actually have to care for it, so I would need to read up on "How to train (and care for) your cat/rabbit".
Despite being an abnormally large feline rabbit, I don't think people would find it too strange. Although it might freak people out, when its yellow rings start to shine in the moonlight.
Well, Umbreon is a really bulky, sturdy pokemon, so I don't doubt it could come to my aid, if I ever happen to end up in trouble. And it would likely be a joy to have it wandering around the house, lightning the mood, and whatnot.
Scizor... That would be AWESOME! He would help keeping my brothers and sisters from annoying me all the time. ( I have 6 brothers and sisters... ) A mansized metal mantis? Only the blind would miss it. As I said, it will keep annoying people away with Bullet punches.