Well not everyone thinks animals smell bad... I think dogs and other mammals with fur smell really good, as long as they're not dirty.
I imagine they'd just smell like their real world counterpart. Pikachu would smell like a regular mouse, geodude would smell like any old rock, etc. I don't know if it'd be wise to sniff poison types, though. --- ACNL QR Codes: http://pikangie.tumblr.com/ 3DS Friendcode: 4597-0805-4383