What wattage charger is best for iPhone 16 Pro Max?

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

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