Today I'll be trying to rank skins based on usability (as in how much it makes you better from that feel and placebo effect) from personal experience and what I've seen pros use, with some recency bias. I'll be limiting it to 3 each, all in order.
Classic: Capsule, Prime, Nocturnum (HM: Spectrum)
Shorty: Oni, Chaos, Primordium
Ghost: Sovereign, Gaia, Phaseguard
Frenzy: Glitchpop, Bolt, Elderflame
Sheriff: Singularity, Reaver, Arcane/Neo Frontier (HM: SoL)
Stinger: Sovereign, Chaos, RGX (HM: Depths)
Spectre: Prime, Ion, BlastX
Bucky: Ion, Radiant Crisis, Origin
Judge: ChronoVoid, Glitchpop, Elderflame
Bulldog: Araxys, Glitchpop, Protocol (HM: Velocity)
Guardian: Sovereign, Prime, Neptune
Phantom: Recon, RGX, Oni (HM: Champs 24)
Vandal: Chaos, Gaia, ChronoVoid (HM: Champs 21)
Marshall: Sovereign, Neo Frontier, Gaia (HM: Ruin)
Outlaw: RGX, Araxys, Phaseguard (HM: Overlay)
Operator: Forsaken, SoL, RES (HM: Imperium)
Ares: Singularity, Ion, SoL (HM: Infantry)
Odin: Evori, Reaver, BlastX
Melee: This is very subjective since it doesn't give that placebo effect as much as regular weapon skins, but my favorite are the the SoL daggers.
There are some close contenders but ultimately I've limited myself to 3. What do you think of this list? Which would you have changed?