I am not a believer in mass gainers. I will always suggest you make your own. This way you can tailor it to your daily macros and overall calorie needs. I would always use a good quality whey isolate like WTBM Isolation. Then, you can add what you chose to it. Muskate gives you some good suggestions. Also, creatine only needs to be supplemented at 5-10g per day in order to keep muscles saturated. Take it pre/post workout and use a nice product like Ancient Strength:
Ancient Strength
The serving amount is 3 tablets and in typical N2BM fashion you get a 30 day supply, so about 90 tabs.
Each serving of three tabs contains:
Creatine Monohydrate………………………………….4,551mg
Creatine HCL……………………………………………300mg
Creatine Pyruvate………………………………………150mg