Every girl is different. Some find the guitar hot. They fantasize about a guy who would play them songs or maybe thats not there thing, just something about it is hot. Some find guy a who play sports hot. Something about the activity (and of course) the fact its a given there in shape, they find attractive.
Also there's something about either the guitar or sports player that puts a personality image into your head. Guitar makes you think the guy know how to act sexy, he's creative and fun, either outgoing and wild or shy and sweet or deep and reserved. Sports player makes you think outgoing and fun, good with people and aggressive (doesn't quit for what he wants), and muscles :D
I think that you should do what makes you happy, and attract girls who would appreciate that. Your in shape and got talent. If you do one over the other you enjoy more, the right girl is bound to tell you to do the one you prefer unless your doing it for something like scholarships.
My opinion? Id prefer a guy who could play the guitar, but id love it if he was still in shape. I dislike the overly muscle type body but just toned and defined i like. Id say go for the guitar, since you seam to prefer it, but stay with the lacrosse if you have fun with that too. If you dont have time for both dont completely give up on the other, at least keep it as a hobby.