Hmm. My vote is for your wife... but you have a good-looking sister-in-law.
Hockey,
Your wife's scantier clothing suggests a more sexual personality, her facial expression suggests she's proud to show off her assets, and her prominently-displayed wedding ring implies "see, I'm a married woman... ya' want it? Come an' get it...". She appears to be a very sensual woman. Also, at 5' 8" she's relatively tall — with high-heeled boots she could be 6 feet. (I like tall women.)
Your sister-and-law, by contrast, has a buttoned-up look about her suggesting she may not be entirely comfortable with her own sexuality. At least, not yet. She looks younger, suggesting (I would guess) she's less experienced and is thus less confident with men. She's very attractive, though, and probably has large potential... if her personality is not "buttoned up."
So, my vote is for your wife.
—Custer