Use cases
The same mechanic breaks differently for everyone
A seven-day identifier is a rounding error for impulse ecommerce and a catastrophe for B2B. Pick the one that looks like your business.
By industry, with the numbers
Same product, whichever one you are.
A durable first-party id, server-confirmed conversions, and a journey you can read. What changes by use case is which part saves you the most money.