If straight-up mass is what you're after, then i recommend BSL Alpha-1 Max. It gives wet gains, so a good bit of water, but this makes you look big. Take 60mg (3 caps) per day, and you will see some Dianabol type size starting to develop within the first week. I kid you not.
It will give great strength gains, and cushions joints, so you can put more weight on the bar, OR use less weight to save your joints, and increase the reps. Either way WILL put some serious size on you.
The intramuscular and sub Q water present during the cycle will give you the strength to make size gains, so even after loosing 6 of 12 pounds, you will be bigger, and stronger for the next cycle.
Methadrol Extreme will put size on you at a slower rate, but gains will be much more dry. Super DMZ 2.0 the same. M-Sten the same. All great stuff, just make sure you use the dose for each that is required for maximum results.