What printers work best with iMac?

Look for ones that say they support AirPrint. Printer vendors have a bad habit of failing to release new drivers to keep up with updates to macOS, with the result that you might update macOS, only to find that your printer doesn't work, and that the company who made it has no plans to make it work. Their solution: Buy a new printer …

AirPrint basically builds enough information into the printer that macOS can print to it without additional drivers.

About AirPrint - Apple Support

There are literally hundreds of printers that work with the iMac.

Which is best is different for each user and depends on what features you're looking for, your budget, the location you want to use it and other considerations. So, you'll have to do some research.

I suggest a printer that supports AirPrint wireless printing.

About AirPrint - Apple Support