What wattage charger is best for iPhone 16 Pro Max?

What do you mean by "proper?"

Per the Apple specs for this phone:

Fast-charge capable: Up to 50% charge in around 30 minutes17 with 20W adapter or higher paired with USB-C charging cable, or 30W adapter or higher paired with MagSafe Charger 

Ref: iPhone 16 Pro Max - Tech Specs - Apple Support

28 Watts or more. You can have as much wattage as you want, and the iPhone will only draw as much as it needs.