Neither, basically. What EMP crash does is adding -1000% recovery debuff. Now, your actual recovery cannot be debuffed so much that it becomes negative, but all those unused percents ARE STILL THERE. So if your total recovery buff (including basic 100%, Stamina, shinies, Serum, RA and whathaveyou) is less than 1000% you don't get any recovery. If it's 1010% you get 10% recovery and so on, until you hit recovery cap.
Serum specificaly seems to have 100% recovery buff (that is extra 1.67% of your end bar per tick) Stamina may add another 50% or so, so you still need 750% from somewhere else.
Recovery Serum, like all buffs, is additive.
What happens with a nuke or godmode crash is that you have a 1000% recovery debuff applied to you. That works out something like this:
100% (base regen)
+ 50% (three-slotted Stamina)
+ 100% (Recovery Serum)
- 1000% (crash)
===========
-750%, which is then capped to 0%
Now, if you happen to be teamed with seven Empathy defenders, it looks more like this:
100% (base regen)
+ 50% (three-slotted Stamina)
+ 100% (Recovery Serum)
+ 2800% (seven three-slotted Recovery Auras)
- 1000% (crash)
===========
+2050% (capped at +500%, since you're presumably an energy blaster)
The Wiki entry on Recovery Serum did not answer my question, namely, does Recovery Serum add to your level of Recovery, or does it boost the existing level by a percentage?
After using EMP, you basically have no Recovery for a bit. If Recovery Serum ADDS to your Recovery, you would then have some, but if it multiplies your existing level by X%, then multiplying Zero by 40% would not help after using EMP.
Anyone know what effect occurs after using EMP?
"How do you know you are on the side of good?" a Paragon citizen asked him. "How can we even know what is 'good'?"
"The Most High has spoken, even with His own blood," Melancton replied. "Surely we know."