I made a few quick comparison tools that all pull from the Armory API and let you compare your achievements, mounts, or pets with another player.

Achievements: http://comp.wowmetacheck.com/
Pets: http://comp.wowmetacheck.com/petcomp/
Mounts: http://comp.wowmetacheck.com/mountcomp/

I know the UI is a bit rough, but they should all be up-to-date with 5.2 and they work quickly and simply. Hopefully someone finds these helpful!