GNC Amplified Mass XXX or Gold Standard 100% Whey?

[david]

I was wondering which one would be the best one to gain weight and build strength and muscle. I am on the leaner side of the body mass and I want to gain a little more weight+muscle+strength. I work out 4-5 days a week. Which protein would work the best for me?

And does the Mass XXX really work? Will it make my muscle "floppy"?

Thank You!