If you care about the planet, the answer is “none”. Wireless chargers are exceedingly inefficient compared to a normal plug and cable. They take up more space, charge more slowly, and waste more electricity. Perhaps, if your household is 100% solar powered, that doesn’t matter.
Just use the charger and cable that comes in the box … wait… oh, right, Apple don’t include one any more.
Now, (if you sell off your old phone or are switching from Android) you have to buy a separate one, with its separate packaging, separate shipping, etc.
In what way is this eco-friendly, Apple?