This is a good thread. It's neat to see what other people are playing.

Most Played:
D&D 3.5 - 12 (ish) full campaigns
Pathfinder 1e - 5 full campaigns
Exalted 3e - 5+ campaigns (currently running)
Masks: A New Generation: - 3 full campaigns (my actual favorite ttrpg)

Sometimes Played:
Mutants and Masterminds 3e - 2 campaigns (not a fan)
Rifts - several sessions (not a fan)
D&D 4e - arguably too much
Ironsworn (big favorite)
Urban Shadows (had a blast)
World of Darkness (terrible GM, would like to try again)
Monsterhearts - several sessions
Tianxia - several sessions

Played Once:
World Wide Wrestling (solid gold, best combat system in ttrpgs)
Dungeon World (rather eat mold)
D&D 2e (don't do 24 hour sessions, kids)
Microscope (excellent session 0 tool)
Shadowrun (absolute slog)

Watched My Friends Play:
Chuubos Marvelous Wish-Granting Engine (sounds fun)
Ars Magica 5e (also sounds fun)

Games I Intend to Play Once, And Die Shortly Thereafter:
Sea Dracula