It's really, really difficult to say one is better than the other.
However, I can honestly say that I lust a lot more after Adriana than I do with Alessandra. When I open a VS catalog the first model I look for is Adriana because she is so incredibly sexy!
I love Alessandra as well but there's something more about Adriana that attracts most men. Maybe it's the lingerie that she's dressed in, maybe it's the poses that she is put in, but Adriana seems to be the PERFECT model for VS lingerie.