You don't need to overthink this. Here's a simple experiment:

Day one: wear your regular fit tee for a normal day—errands, maybe a casual meetup. Notice how it feels when you move your arms, sit, and reach for things.

Day two: switch to the oversized fit. Same activities. Pay attention to whether the extra fabric bothers you when you lean forward or put on a seatbelt.

By the end of the week, you'll know which one you naturally reach for. And if you're still torn, think about what you're doing most: if you're chasing comfort at a desk or on a couch, oversized wins. If you're active or want to look put-together without trying, regular is your friend.