What is the best wattage charger for iPhone 11?

There isn’t a best one.

Here are the rapid chargers specifically mentioned by Apple: Fast charge your iPhone - Apple Support

Rapid charging with any of the listed chargers will usually get a drained iPhone 8 or later to 50% charge well within an hour.

Apple 20 watt.

It’s Apple’s 18w fast charger, 20w fast charging is not supported in IPhone 11, hence still if you use 20w fast charger it will give you the same charging as 18w fast charger.

My suggestion was an answer to the OP. An 11 can use the 20 watt and it will last until the next device.

No only use that charger with which mobile is compatible or else use less watt charger but Apple’s genuine one.

Anyone with a glassed backed iPhone (8, and up) can use a MagSafe charger on even their laptop 96 watt charger if the want.

The circuitry of the battery prevents overcharging.

Lol 😂