First up, my personal favorite out of the three, part 2:
Why is this my favorite? Because I learnt how to differentiate the members of T-ara using it (on hindsight, it's not a good MV for doing that).
And then there's part 1, the normal version with makeup scene and dancing scene, complete with 2 sets of performing outfits.
This should be the one most are familiar with.
And finally, the part 3:
If you watched all 3, you'll realize that parts 2 and 3 are essentially the same thing:
T-ara singing to their reflections in the mirror; the only difference is that for part 2, the camera films the reflections whereas for part 3, the actual members are filmed.