Ive never used calcium caseinate, I always use micellar casein mixed with low fat milk and I never have stomach issues with it. And I usually have some slight stomach issues with 100% whey isolate protein.
Micellar casein has seemed to be the best bet for me as far as stomach issues, but if youre lactose intolerant than that still wont matter.
I have also heard that beef protein powder is good for those who get an easily upset stomach (i think true protein sells it)