Seen both (Julia only once, some time ago and before she moved to Vancouver).
See my review on PERB of Alexis, as well as DaPup's recent review of Alexis which is consistent with my earlier review.
I think you'll find both are beautiful women but beauty is in the eye of the beholder and so it's really up to you to judge for yourself who is the more attractive by reference to those features (face, skin, firmness of body, breast size, etc.) that are most important to you from your own perspective.
Personally, I don't think Alexis' pictures do her justice and I find Alexis much more beautiful in person than comes across from her pictures.