ive bought both... and i'm 5'3" at about 130lbs... small chested... and the guys small shirt is a little baggy... not much...but i think i prefer the girls large over it... the guys is kinda long and the sleeves are a bit big on me... if that helps your decision any...

I once ordered a guys small AND a girly medium at once to try them both out, see which one's better, and I like the girls one. The guys shirt fit okay...The sleeves looked a bit weird, and the fabric around the waist was kinda big and poofy. But the girls medium (don't know if it would be the same for all sizes in girls t's) fits quite well--form fitting, but not so form-fitting that any little bulge looks nasty, and the shirt is long enough so that it doesn't creep up on you a lot. I'm 5'5 and I always get the medium.

Hopefully you can apply this information to yerself! :)

I'm 5'2", and 90 lbs. I think the girly small feels great and fits perfect. It is not tight (only a little snug around the chest, but for my size i have a wide chest).
On my profile there are two large pictures of me in my shirts.
The "Something we guess not" shirt is unwashed and dried.
The "<3 destroy" shirt was been washed and dried.
Hope that helps!! :)

I'm 5'3" and 140lbs, but I have massive boobs.
The mens' small fits well, but is a little snug around the boobs. I have some girl shirts on the way (prolly next thursday or friday), but I don't know how they fit yet.

I'm not a girl, but i have a girlfriend who I get Threadless shirts for and I would definately say a girls small for you.

i'm 5'8"/120 lbs, and i get girls smalls and mediums, so i think you should get a girls small.

I'm 5'3" and 150 with 36C ta-tas.
For what it's worth, the Girls Med is cozy but fits, the Girls Large is better but shoulders a bit too wide. But I think the Girls shirts are curvier than the Guys fit, so curvy girls should go with that, right?

About a year or so ago when the men's shirts were the American Apparel brand, the small was the perfect fit for me ... but since now they use the Fruit of the Loom, they're too big. The girlie large is okay, but the sleeves are shorttttt and the body is shorttttt, and I sure wish there was a men's extra small, or something. I'm 5'4" and 125lbs.

You'd probably do fine with a girl's large ...

thanks for all the help! i'll be ordering and tell you guys how it went!

p.s. are the white t-shirts also kinda see through?

I don't own any white t-shirts from Threadless, but I do have a few light colored t-shirts (banana, light blue, creme). if you wear a nude-colored bra underneath, nothing will show.