From what Ive read you need both in a night time protein drink you need the fast acting Whey for the initial hour or so of sleep then the Casein and Cesinates give a slow release.
You also need something to give a slow release of insulin.
http://www.findarticles.com/p/articl...20/ai_98488573
Most of the night time proteins Ive checked up on contain Whey protein Isolate as well as Casein.