If you want to switch between versions on OSX I find it's easy to do with just homebrew. If I want to switch to PHP 5.5 I type `brew link php55`, I want PHP 5.6 it's ... you guessed it ... `brew link php56`. Very simple.
I also use MAMP stack to switch between versions for the browser which is just "out of the box". I will, however, being moving away from MAMP and toward NGINX/FPM but my command-line solution then should work fine. I think where it really becomes complicated is when you want to run multiple versions at the same time on the same machine. For instance, to have one app using 5.4 and another on 5.5. Hopefully this is an uncommon requirement for most but I imagine some people run into it and I don't have any good answers for that.