I use nvim -D which is a lot like vimdiff. Few tips:

• if the color scheme is unreadable, try :set termguicolors
• dp to push a diff chunk to the other file
• do to obtain a chunk from the other file
• I have alt+hjkl bound to switch windows, which is nice

It works really well for me, I haven't wanted anything else. I'm one of those weirdos who spends all day using neovim, though

meld really is my favorite, but there's also mcdiff from mc, in combination with your editor of choice (use_internal_edit=false). If you can like the internal editor, though, that's got to be a better experience.

I find a bunch of the themes are unreadable, so am rotating and eliminating with this Zsh function:

mcdiff () {
  emulate -L zsh

  local skins=(
    gotar
    gray-green-purple256
    modarin256-defbg
    modarin256
    modarin256root-defbg
    modarin256root
    sand256
    seasons-autumn16M
    seasons-spring16M
    seasons-summer16M
    seasons-winter16M
    xoria256
    yadt256-defbg
    yadt256
  )

  local skin=${skins[RANDOM % $#skins + 1]}

  print -rl -- "Using skin: $skin:t:r"
  =mcdiff -c -S $skin $@
}

For a non-interactive diff viewer I find riff's output pretty legible.

Other than that, I've used a combination of tools with a broot config to browse and manage the diffs...