I really don't like my wii (yeah, insert joke), but think the Miis do a better job than the avatars. I agree with the idea I've seen elsewhere that the simplicity and lesser options of the Miis actually allow you to approximate real people a lot better.
Plus the wardrobe choices are all totally douchey.
Hmm... I would like my avatar to be wearing a gears of war soldier outfit. Now THAT would be badass. Or maybe a Viva Pinata outfit o.o; Oooh. That'd be great if they released outfits of game characters for your avatar to wear. That'd be total win!