whats the best weight gainer people on this site have used?
Most are a waste of money and overloaded with sugar and low-quality protein.
You're much better off spending your money on real food (can't stress this enough), quality protein powder (Grow!), and post-workout nutrition (Surge).
The vast majority of people on this site really disapprove of weight gainers for exactly the reasons mentioned by Atmosphere.
In fact, I'm surprised to hear that they're still making them. Well, scratch that; nothing really surprises me much in this industry.
I suggest trying search. This question was just asked, more than once, recently.
Beef works well for me.