I went Nerve myself, at least for now. With Power Boost it gets me to the soft cap. Nerve was also a sizeable increase in Acc for the Drones and Prot bots too, as I slot them for more than just Dam/Acc.
Don't forget that Musculature boosts all of your pets' damage. That's more than three powers, imo. Still, it only gives like +20% max after the ED cap? That's less than one small red. It's one small all the time, but that didn't seem that big of a deal to me. Anyone else?
Cardiac and Nerve I haven't really thought about. I personally have enough End (I got a lot of +Rec in my IO sets.) Recharge on Bots/FF seems dubious to me. There's very little need for recharge that I can think of in my build.
I'm a Bots/FF MM and have Nerve Core Paragon (Very Rare) and Musculature Total Core Revamp (Rare, will become Musculature Core Paragon next week).
Reasoning? You can fix endurance problems with IO sets, recharge doesn't affect henchmen (and as FF, recharge is of limited use anyway) and IO sets can't grant accuracy or damage to henchmen.
Remember, each henchman represents 3+ attack powers apiece - anything you can do to boost that output (in Acc or Dam, as you can't with Rchg) is all to the good.
I can see some argument for Spiritual or Cardiac with other secondaries, but not with Forcefield.
In a team setting I use Nerve (for the defence boost to Forcefields) and solo I use Musculature (to bump up my solo damage). Once I have my Barrier Destiny up to a reasonable (Uncommon+) level I'll probably be less inclined to use Nerve for the defence, but the additional accuracy for Ionic Judgement will be hard to give up (maybe once I see it with Musculature instead...)
Edit: for point of reference, my build to date which has no endurance issues, except during initial summoning
I finally got a red side to 50.
I wont talk so much about how long it took me, as he has been my 'focus' character off and on. I like to think he was spending time in his lab developing new technologies and weapons and only came out to do mayhem and rob banks when funds were getting short.
I can kinda see the point for all of the Alpha options. Each would help.
Cardiac - I run 5-6 toggles. With those going it is difficult to bubble my bots or team members and not end crash. There is still much I could do with unique IO's and sets to fix End however.
Musculature - More damage is always good. But really, this would only increase five powers and that is counting force bolt. Run speed, Immob and defense debuff do nothing for me. End mod is t4 only.
Nerve - More acc would mean more damage. The level shift acc mods for lower ranked pets would be less of a problem. Fly speed and Defence Buff also would be good (I use hover). Defence Buff would stack from both myself and my protector bots.
Spiritual - More recharge, like more damage is always a good thing. The only abilities I seem to really have to wait for are 'Surge of Power,' 'Em Pulse' and maybe during a nasty ITF 'Personal Force Field.' Moving slots around, this being my only character that seems to have slots to spare, would fix a lot of that, if I were worried as those arnt real key abilities.
Have I missed any key points for or against each Alpha specific to a Bot/FF mastermind? It seems in my best interest to go with Nerve which is funny in that when I first read about Alpha abilities and even on my blue side people who have them, I never thought Nerve would be useful except maybe on a controller - and mine needed cardiac far more desperately.