seeking wisdom Scrapper incarnate Alpha slot

Just dug out my BS/regn scrapper, what is the current thoughts on the best Alpha slot for him ?

Without actually seeing your build, probably Spiritual. If not Spiritual, Musculature.

On my recent scrappers I consider the red musculature icon amid the sea of other icons on the team window to be a badge of excellence. It shouts to the world (of your team) that your build already has enough recharge, endurance, and defense! You didn't want any help with those! Nay, friend, what you wanted was more damage. And you got it, thanks to musculature.

For BS I suggest muscularate but than again anything on a scrapper usually gets most out of muscularate maybe except claws. Think this way which is more important. %30+ damage or %30+ something else. Since 2/3rd of alpha won't be ED you will get at least %30 (most probably %35 but that is subject to change) from a T4 of %45 and considering that BS is one of the highest burst damage sets (if not the highest scapper one) I think you will get more DPS out of muscularate.

As far as I'm concerned, when it comes to /Regeneration, there is no such thing as "enough" recharge or Healing so I will always recommend Spiritual first.

As for the rest of the options?

You're /Regen so you'll never need the Endurance help from Agility, Cardiac or Vigor.

You're /Regen so the Defense and Resistance bonuses from Nerve and Resiliant do not help very much.

You're /Regen so you're probably already running Tactics so you don't need the Accuracy from Nerve or Vigor.

You're a Scrapper so you can't Hold anyone so Intuition is pretty much useless.

That leaves Musculature, which is a good option, especially for BS with it's inherent Defense DeBuffs.

TL;DR, I prefer Spiritual for all /Regen characters but Musculature is a good option too.

I agree with Spritual Core Paragon (Recharge and Heal intensive) first. I would also get Musc as an alternate they are easy enough to get with some time investment (but you'll have to do some trials, obviously)