Both work quite well, as superdrollover mentioned.
Since you are only going to be using one bottle, it seems, I'd recommend MassFX.
The reason being is that it's effects start working faster, making it a little more noticeable for gains in the short-run. As for a long run, gains will start to slow down after around 6 weeks, making MassFX your better option for shorter cycles.
For a longer cycle (more than 4 weeks), hyperdrol is your friend. It takes a little longer for the effects to build up. The gains pick up speed very gradually, and stay there for a long time, oftentimes for a week or two after cessation of the product. Decent gains for a short run, but much better gains for a long run.