What is best to do, shut down or use the sleep mode?

You are welcome.

For more about Sleep mode:

Sleep

Put your Mac to sleep or wake it

When you’re not using your Mac, you can save energy by putting it to sleep. When your Mac is in sleep, it’s turned on but consumes much less power. It takes your Mac less time to wake from sleep than it does to start up after being turned off.

https://support.apple.com/guide/mac-help/put-your-mac-to-sleep-or-wake-it-mh10330/11.0/mac/11.0

Some Mac notebook computers have a feature called safe sleep. With safe sleep, each time the Mac goes to sleep, the current state of the Mac is saved, including open apps and open documents. Safe sleep prevents your information from being lost if the Mac is completely shut down during sleep, which could occur if the battery runs down or is replaced.

https://support.apple.com/guide/mac-help/what-is-safe-sleep-mh10328/mac

Energy saving

https://support.apple.com/guide/mac-help/save-energy-mh35848/11.0/mac/11.0

About Shutdown mode:

Section: Shutdown

https://support.apple.com/guide/mac-help/log-out-sleep-wake-restart-or-shut-down-mchlp2522/11.0/mac/11.0

Whichever is convenient at the time. I always shut down, mainly because I don't stop my work mid activity. I also like to clear cache by shutting down. But many here use sleep mode.

Use in Sleep mode. Newer Macs do not need to be shut down constantly as older ones did.

But once in a while restart the Mac.