My favourite is not really a breed, but Domestic Medium Hair. I like everyday cats that you see all the time, and medium hair is definitely my favourite. Next is probably Ragdoll. I think Maine Coons are really pretty too, but since they get so large, I would probably never own one. I like my cats to hover around the 10 pound mark.
Edit: I just looked up Siberian cats...they might be my number 2--very pretty!