im not a fan of stricly GNC whey proten products.. never liked them...... but i imagine this could be a good one..
so i would go with ISOPURE its a cleaner whey protein... its cleaner and not as much junk in it.
GNCs might have more junk and sugar in it...
but then again u want to eat more calories to bulk up... so dont just rely on the shakes... u have to eat alot more food