Psycho Cut/ShB has higher DPs under about level 25 and over about level 32, which may be slightly different depending on your attack IV. Confusion gains a slight edge in the upper 20s. This is assuming no lost energy, which would hurt psycho cut/shb more. In a legendary battle, where mon don't last long and dodging is difficult due to server lag, I would guess the performance would be similarly above the last PC breakpoint.
SB Mewtwo for Giratina Raids
Background: I don't have any Salamence or Rayquaza (haven't got enough candy to evolve my first, and missed raids last winter). I only have 2 dragonite (evolved and powered both from scratch - missed dratini community day).
So, with the supreme counters out of the way, I move on to the good counters.
Shadow Ball Mewtwo is listed, with Psycho Cut.
Except in the article about Mewtwo's movesets, it specifies that Confusion is better than Psycho Cut unless Psychic is resisted (or there's a double weakness).
Giratina is single-weak to Ghost, and doesn't resist Psychic. Shouldn't that mean Confusion-Shadow Ball is the optimal Mewtwo moveset to take it on?
If not in general, surely in Windy weather (what I had today), Confusion is better than Psycho Cut? (Of course, the dragons would be best, but as I began, I only have two Dragonite and of course they lead my battle party).
Other options:
Level 36.5 and level 35.5 Dragonites
Level 40 SB Mewtwo
Level 34 SB Mewtwo
Level 40 SC/SB Gengar
Level 36 BCr Tyranitar (my current team, mostly wanting ordering)
Potential subs:
Level 40 Meteor Mash Metagross (should I use this in Snow?)
I have other stuff that may be usable (e.g. more shadow ball mewtwo) but don't have the stardust to power it up (down to 24k after powering up the Metagross and my Dragonites, among maxing my best pokemon to 40 after leveling up - ouch).
Answers
Psycho cut charges energy faster and is way easier to dodge with, so unless the opposing mon is weak to psychic type attacks i would use Psy cut rather than Confusion, since the bulk of the damage is done with shadow ball. Anyway there's a really small difference that only speed raiders or people who intentionally short man the raid can notice and make use of.
MM metagross in the snow (not the best but useful) and Gengar Sc/SB and B/C ttar are more than serviceable, Gengar can even out dps Mewtwo!!