I've seen too many ways storing everything as UTC goes wrong/gets confusing. Round-tripping at least UTC offset (which unfortunately Postgres `timestamptz` in this case does not do and is effectively the same as storing as UTC) gives you more debugging tools for events in the past and more opportunities to do the right thing for future events in worst cases (strange, unexpected DST shifts). The best option is if you can also round trip exact time zones such as IANA strings like "America/Los_Angeles". Even fewer databases support that natively right now (as a single optimized column).
When UTC offsets roundtrip you can do all your date math as if everything was in UTC, but still not lose information from the user about what time they thought an event occurred at or might next occur at.
When UTC offsets roundtrip you can do all your date math as if everything was in UTC, but still not lose information from the user about what time they thought an event occurred at or might next occur at.