Alpha for SS?
Agility.
Depends on your secondary, but it's hard to argue with moar recharge (and Def and better End Mod).
Cardiac (End reduc, partial Resist) is worth mentioning, if you've already got a recharge-heavy build, you can worry less about end reduc. Usually I view it as kind of a cop-out but some builds really benefit more from that than any others. If you're Willpower, consider Vigor for much the same reason.
If you're Electric Armor or Energy Aura you might consider Spiritual - it improves your Regen rate, and the extra Recharge helps get your clicks up sooner. The recharge also means more damage.
-Proud leader of Captain Planet's Magical Friends
If you're good on HP and recharge, go for Agility for the Defense and Recovery boost
If you're already rocking monster defenses, and your recovery is such that you can GAIN endurance during a fight, go Spiritual.
Musculature, simply isn't worth it for the picayune boost it gives you. And, on leagues where damage buffs fly thick and heavy, it does exactly BUPKISS for you.
Muscle on a brute is almost never worth it (great dor other ATs though). With agility you gain recharge and defense. So more damage and Survivability. Regardless of sexondary. It's my go-to alpha on my brutes.
Yeah, I'm going with Agility.
At this point...the only reason I would want Musculature is for the Judgement damage boost...but I don't use Judgement enough to select an alpha for that sole reason.
Which, in your opinion, would be better for SS...Musculature for the flat damage boost...or Agility for the +rech?