Faster Press and Hold Character Picker
The "Character Accent Menu" settings can be adjusted under: 

System preferences -> Keyboard -> Delay Until Repeat

If you reduce this time, it's the fastest way to insert any accents in my experience. Setting the initial key repeat rate is the same as setting the time for the character accent menu to appear. With this solution, there is no need to change to international keyboards etc (see the other answers). see here. 

If you set it to the minimum value, the delay will be 15 ms, which should be quite fast. However, there seems to be an actual delay of about 300 ms until the menu appears (maybe displaying the menu takes a while? Don't know). 



There's people using scripts to set the delay from 15 to 1 ms, but I'm not sure whether this helps: see here: github.com/mathiasbynens/dotfiles/blob/master/.macos, the relevant parameter is InitialKeyRepeat