SA's are random stat increase at a small cost early on with no fed benefit.
Entrances add additional stars to your fed matches which increase the feds ticket sales while adding a small bonus to your fan gain.
Thing is most GM's want there members to only have Entrances, I agree with this to a point. Entrances help feds out A LOT, however, if you know how to build a char and use the SA's correctly they can be a income as well. SA's activate in tag matches where Entrances don't so SA's could be a bonus to match count creating more exp. However, if you use SA's you will level quickly decreasing the amount of title defenses you receive in each level. I won't complain if a member has SA's however if you don't honestly understand the way SA's fully work buy entrances for your safety as you will earn exp quickly. It'll be worth it more in the long run. If you know how to use SA's go ahead and use them.