There's basically 2 theories I've heard on centralized site growth, both by very intelligent people.
Zyglamail thinks site injections work by raising IGF-1 levels at the injection site. IGF-1 is necessary for cell growth. As for which AAS would work best, any that elevate IGF-1 levels extremely, with tren being the best at doing so.
Fonz says site injections don't work, and may be detrimental to your gains. I think he said the centralized growth is due to swelling and prevents the muscle from healing faster which in turn doesn't allow you to train the muscle as hard. Site injections work for a short time, due to swelling, but subsides eventually.
So believe whichever theory you would like I guess.