I would vote for either:
Gain Structure: It’s intuitive for players and matches how most people search for tones.
-Clean,
High headroom, minimal breakup. Fender, Roland JC style amps.
-Edge of Breakup / Low Gain
Touch sensitive, blues, roots rock, classic breakup.
-Mid Gain
Classic rock, hard rock, pushed British tones.
-High Gain
Modern rock and metal, saturated distortion.
-Extreme Gain
Death metal, djent, ultra tight or compressed amps.
Or
Era / Design Philosophy: Helps
explains why amps feel and respond differently.
-Vintage American
Tweed, blackface, early clean platforms.
-Vintage British
Plexi, JTM, early Vox.
-Hot-Rodded Classics
Modded Marshalls, Soldano era designs.
-Modern High-Gain
Multi-channel, tight low end designs.
-Boutique / Experimental
Dumble, Trainwreck, rare or niche designs.