I use the Canadian version of all the whey. I like the Isolate that uses stevia. No garbage in it, mixes great, tastes great. My fave is mixing banana with strawberry. =D
ATW has a Stevia-sweetened Isolate? That is news indeed!
The only difference between all the different proteins is the time they take to digest. Whey is the only way to go because whey protein digests immediately. Remember, if you're trying to bulk up, it's better to try a mass gainer (True Mass and Cytogainer ftw), don't do Mass-Tech by MuscleTech btw. If you're truly trying to add mass, you also need tons of food, more than you would normally eat. Go to Bodybuilding.com, there are several mass gain diets you could benefit from.
Um, no they don't. Gainers suck: overpriced maltodextrin plus whey concentrate = empty calories with massive insulin AUCs, resulting in fat gain with no nutritive value other that a bit of protein. Just eat calorie dense, nutritive food - avocado, coconut, nuts, olive oil, homemade chili, etc.
BB.com's advice is rarely knowledgable. I have read so much garbage in their "articles" I don't even know where to begin. There are occasional exceptions and I get really excited about those, but they are a rarity.
Additionally, whey doesn't digest "immediately." It takes about ~40min to begin hitting the bloodstream, IIRC. If you mean it begins digesting immediately, well that is true of every food you eat - they all begin digesting as soon as they hit the stomach, they just are processed at different rates.
I don't mean to be negative, there just happened to be a lot of things in this post I disagree with. Nor should you take this as a personal attack.