It depends on what I'm doing.
Baking: metric - grams on a food scale help me replicate recipes perfectly.
Cooking meat: standard - 140°F steak, 165 chicken
3D printing: metric always
Woodworking/household: standard - inches are just the standard for all the things. Wood, curtains, hardware, etc
Mechanical: ??/?? Depends on where it's made! I hate having to switch wrenches or sockets due to the wrong standard.
This is actually pretty neat. Great replacement for doomscrolling.