I switched to coding in a proportional font, Verdana, a couple of years ago and never looked back. That's the font you are reading this comment in, in fact. Code is mostly words and words are much easier to read in a proportional font. Symbols are plenty clear enough in Verdana, all letters are distinguishable, and I don't use mid-line alignment so I don't see the point in a monospace font outside of the terminal.
What language are you using such that inter-line relative column spacing doesn't affect your code comprehension? > I don't see the point in a monospace font outside of the terminal Why not use Verdana in the terminal?
edit: and maybe Haskell? the layout rules are complicated
personally I don't think lining up e.g. variable or parameter names in c style declarations improves readability at all, and it pollutes git diffs.
but I do use a monospace font in the terminal because many command line applications align their output into columns using spaces.