Shutdown or sleep on imac ?

In the last week i have migrated from pc windows machines to a 2010 imac.
Its working great and really pleased with it.
On an average day i probably access it 4-5 times a day.I am retired so am home most of the day.
Is it best to shut down or put it into sleep mode when it have finished?
I am used to turning off my machine each time especially at the end of the day.

Sleep.

- Nick

Your iMac operating system (Mac OS X/Mac OS/macOS) will perform routine maintenance when not being used. It will usually perform these things when left on overnight. There are daily, weekly, and monthly scripts the OS will perform, if the machine is on and not in use.

For a slightly different view, I live in a sub-tropical area noted for thunderstorms.

I leave my iMac sleep unless there is any chance of a storm, then shut down computer and modem, even they are connected through an Uninterrupted Power Supply. (UPS).

i put mine on sleep rarely shut it down, or restart it.

This topic (and others from new switchers like yourself) has been covered many times over, you might want to browse the Switchers Hangout forum and do some searches for the wealth of information that is already present..