The Venetian was there first. It is more themed. Venice and all. The Pallazzo came next, it is more contempory. Both hotels are owned by the same corporation and the hotels are connected by interior walkways, shopping mall style. The bigger shopping mall and most of the attractions (Madam Tassauds etc.) of the property are on the Venetian side. The Pallazzo shopping mall is pretty quiet and very upscale. The rooms are pretty much the same layout, just different decorations.
Just guessing, but I think young girls would rather be at the more active Venetian, more going on besides upscale dining and gambling. The food court is at the Venetian. The spa is the Canyon Ranch, again at the Venetian. Pallazzo is easy parking, easy in and out.