Bug Bite VS X-Scissor: When to use which combo finisher
First things first, lets acquaint ourselves with the basic damage values of Bullet Punch and its follow-ups.
-Bullet Punch (all 5 hits, no followup): 60
-Bullet Punch > X-Scissor: 108 (124 with successful just frame)
-Bullet Punch > Bug Bite (only true if Bullet Punch hits an aerial opponent): 130
Now lets see the use of these finishers in Scizor's trademark combo:
-5YY > 6AA > 6YX > 4Y > 2Y > 1A~X: 184 (186 with just frame)
-5YY > 6AA > 6YX > 4Y > 2Y > 1A~Y+B: 208
And a jump in combo:
-jX > 6YX > 1A~Y+B: 170
-jX > 6YX > 1A~Y+B: 148 (150 with just frame)
So it seems that Bug Bite is always gonna be your go-to mid-screen finisher, but how about the wall? Lets take a (very) basic wall combo that allows for both follow-ups.
-5YY > 6AA > 2X > 1A~X: 198+30 (200+30 with just frame)
-5YY > 6AA > 2X > 1A~Y+B: 220
This is more interesting. Ending in X-Scissor deals more total damage, but the last 30 damage of it can not kill. Ending in Bug Bite deals more true damage, but less total damage.
That being said, there is a better combo that only allows for a x-Scissor finish:
-5YY > 6AA > 6YY > 1A~X: 203+30 (205+30 with just frame)
And on some characters (expect a specific list from me soon) you can do this for more damage:
-5YY > 6AA > 6YX > 6Y > 1A~X: 210+30 (214+30)
Cant quite reach the true damage of the Bug Bite finisher, but X-Scissor is usually better as it leads to more total damage.
Long story short: Use Bug Bite as your primary combo finisher, but at the wall X-Scissor is usually the better option