I use IBM Plex Sans (proportional) as my default Emacs font, with variable-pitch as a no-op (i.e., defined as "(variable-pitch ((t nil)))" in custom.el), and use IBM Plex Mono as fixed-pitch.
Tips for using a variable pitch font as the default:
0. Choose default fixed and variable pitch fonts with identical baseline-to-baseline heights for a given size; this makes everything described below work better (e.g., this is true for all fonts in the IBM Plex family across all platforms I regularly run GUI Emacs on [Linux, Mac, Windows]).
1. Define a fixed-pitch-mode by copy-pasting the built-in variable-pitch-mode and making the obvious changes (both are trivial applications of buffer-face-mode).
2. Add fixed-pitch-mode to hooks for modes that don't play nicely with variable-pitch fonts (calc, dired, hexl, magit, terminal and shell modes, etc.), or where you just prefer fixed-pitch modes (hint: define your fixed-pitch-mode in a package so you can use use-package's ":hook ((foo-mode bar-mode … baz-mode) . function)" syntax to manage this).
3. Some modes that pop up windows (frames in Emacs parlance) within editing buffers require extensions (e.g., company-posframe-mode for company-mode) to work properly in variable pitch buffers.
4. Last, but certainly not least: assign a convenient key binding to toggle fixed-pitch-mode. I can't emphasize this enough! In fact, I've found that variable pitch is fantastic for coding in most languages if and only if fixed pitch can be quickly toggled on and off with a keystroke, iff this setting is per file rather than global (and iff both fonts have identical line heights, but this is a feature of font families rather than editors).
For this reason alone, I'd argue that Emacs supports variable pitch fonts better than most text editors.