A website logo should be simple. It should be visually appealing when it is in different sizes: 64x64, 32x32 and 16x16 pixels. Often time, the logo is beautiful when it is big but unrecognizable when you shrink it to the browser tab height, i.e 16x16 pixels. Therefore, a logo should have less demarcations and colors.
Use SVG file for your logo
Using SVG file for your logo is the best. The quality of your logo will not be affected when users
zoom in or zoom out.
In Drupal, from the UI, you can't upload a SVG logo file. The only allowed file formats are: png, jpeg, jpg and gif.
What you can do is to manually overwrite
/themes/YOUR_THEME/logo.svg with yours.
Don't forget to change
/themes/YOUR_THEME/favicon.ico too. It is the icon shown on the browser tab.
You can use ImageMagick to convert your image to
favicon.ico. You can find the conversion command here.