Windowed. When i was new to the game i watched an episode of the osu!academy(https://www.youtube.com/watch?v=j8fpJKCjTvM) where ztrot mentioned the fact that you have to move around less with a smaller window.
Since then i've been used to it and whenever i try fullscreen nowadays everything feels too big and far apart.
Windowed when I'm playing Taiko and Mania, because I just prefer it that way Full screen when I'm playing Standard, because my mouse moves too fast in windowed mode, even though raw input is activated
Fullscreen. I never play anything any other way, unless I don't have a choice. I have terrible ADHD, so if there is something else to catch my attention, it will.
Also, I like to keep the resolution in a 4:3 aspect ratio. It helps when you need to spin, and also the playfield is limited to a square anyway. I think this gives it an advantage.
Fullscreen ,because each time the windows switch wallpaper my latency became over 300, but it doesn't happen on fullscreen and also I am more accurate when on fullscreen