Are hanging tree air fresheners or vent clips better?

It depends on what you want. Across verified-purchase reviewers, hanging cardboard fresheners like Little Trees are praised for being cheap, strong out of the package, and easy to swap, but their scent fades within days to a couple of weeks. Vent clips such as the Febreze line tend to last longer because airflow drives the fragrance and many have adjustable intensity. Vent clips cost more per unit but generally meter their scent over weeks rather than days.