Ale signs should take precedence over gitgutter, that's also how syntastic and gitgutter work together with syntastic taking precedence. the idea being as I fix my syntax errors, I'll be able to see my gitgutter signs. Especially important because I should be fixing syntax errors before committing code (which would clear the gitgutter signs)

Here is a related discussion on this for gitgutter and syntastic quite some time ago airblade/vim-gitgutter#1