what's the best image converter for mac?

The command-line sips utility can convert between all formats you mention without needing third-party software.

man sips
sips --formats

Convert images for the web using the Sips command line on MacOSX

And there is Graphic Converter 12 for a visual interface with batch conversion capability.

The built in Preview app can convert between HEIC, JPEG, JPEG-2000, OpenEXR, PNG, PDF and TIFF directly.

click here ➜ Convert image file types using Preview on Mac - Apple Support

If you need more than what Preview offers, another option is Gimp. It has support for a vast number of file types including GIF, WebP and other formats.

https://www.gimp.org/

I use Graphic Converter 12, as Viking suggests, but Preview will do it also if you like simple (as I do).

https://osxdaily.com/2010/01/24/convert-images-in-mac-os-x-jpg-to-gif-psd-to-jpg-gif-to-jpg-bmp-to-jpg-png-to-pdf-and-more/

From other posts lately, it seems Preview may not be as compatible in newer OS versions as it was when the 2010 OSX Daily article was written. It appears Sonoma dropped eps support in Preview:

No icon preview for eps-files in Sonoma - Apple Community