I've tried many many different brands and I've dealt with a lot of stomach issues. The best I have found so far is Dymetize elite whey. Great price too. http://www.thebodybuildingshop.com/dy2060062.html
ISO AGB from the AF Store.
Highest FDA digestibility rating
Highest isolate protein percentage
Contains Acetyl l Glutamine so you don't have to supplement it.
ISO AGB was my final solution to some serious searching for a protein that did not cause gastro intestinal distress AND fit the exact profile i wanted for my protein supplementation.
I occasionally mix it with Muscle Milk purely out of flavor addiction to some MM flaves, but of late have been adding Ground Fresh Cinnamon, Vanilla Paste and Dried Orange Peel to ISO AGB: flavorgasm. A little oatmeal powder to add carbs and thicken the consitency and some frozen coffee (i pour the rest of the pot into ice cube trays) and i have a smooth love fest that would bring tears to yer eyes...
my fiance has the same problem....i gave her my ON whey gold standard and didn't sit well with her at all. she started using mhp's probolic...it's a mix of whey, casein, and soy....has no problem. to much whey isolate is not good for people with weak stomachs or someone that is lactose intolerant