Is this be the best 'test' to use if not why not? (for gaining mass)
test is test. personally I like cyp and enan is a great choice as well. not much difference. I prefer a single ester or a blend like sust
What doses is it most effective?
generally 500mg week minimum for growing/mass phases.
What do most people run it with to keep sides down? (estrogen)
you shouldn't need one at 500mg or so. Aromasin if you are stacking a lot.
How much mass do users put on while on this 'test'?
depends on your diet, training, and current development.