what wattage charger should I use for the iPhone 17

20 Watt will work nicely. 40 Watt and higher if you will be needing to fast charge the iPhone.

If you ask me I would prefer 30watt charger. Not slow but not the fastest. 40 watt chargers are game-changer with their speed but it makes your iPhone too hot the handle and slowly reducing it's battery life (not a big deal).

if you don't care about fast charging then you can go as low as 5watt

If you want to fast charge, see the following from Fast charge your iPhone - Apple Support

For iPhone 17 models, you can charge up to 50% battery in around 20 minutes with a 40W adapter or higher.