Greetings bob410,
Thanks for visiting the Apple Support Communities! It seems you're curious which power adapter you should use to charge your iPhone, and if it's OK to charge your iPhone overnight.
You're welcome to use either the 5W or 12W power adapter. Check out the information in the following article: About Apple USB power adapters - Apple Support
You may also be interested in using Optimized Battery Charging to help improve the battery lifespan:
About Optimized Battery Charging on your iPhone - Apple Support
"With iOS 13 and later, Optimized Battery Charging is designed to reduce the wear on your battery and improve its lifespan by reducing the time your iPhone spends fully charged. When the feature is enabled, your iPhone will delay charging past 80% in certain situations. Your iPhone uses on-device machine learning to learn your daily charging routine so that Optimized Battery Charging activates only when your iPhone predicts it will be connected to a charger for an extended period of time. The algorithm aims to ensure that your iPhone is still fully charged when unplugged."
Regarding the battery health: "A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge. Learn more about charge cycles." - iPhone Battery and Performance - Apple Support
Kind regards.