Thanks.
T-bol is OK...it produces mild, dry gains, but it's also mild from a toxicity and external side effect standpoint.
SD gives the best of both worlds. Its both a hardening/drying drug, and also a mass and strength gainer par excellence, but it displays above average toxicity, can suppress appetite, and makes some guys feel lethargic and shitty. It is great for increasing fullness while staying hard and dry, which is why some people use it pre-contest. It is better than Anadrol for this purpose.
No steroid produces more maintainable better gains than another--some just causes more or less intramuscular water retention. Because this water is inside the muscle, it looks like legitimate muscle, so when you go off and lose that IM water, you shrink. But unless you consider water to be "gains", there really isn't much of a difference between the various AAS in terms of keepable "muscle". Now, some steroids may cause a degree of glucocorticoid rebound upon discontinuation, which may affect gains retention to a degree, but this effect is relatively minor, at best.
SD does cause a LOT of real muscle fiber growth, though, so most guys will be left with a pretty good amount of mass after all is said and done--certainly more than a drug like Anavar or Winstrol, as those drugs just don't build as much lean tissue to begin with..at least compared to SD. However, because drugs like Var and Winstrol don't cause nearly as much IM water retention, you won't change as much when you go off (in terms of size).