Depends on how much time you want to invest in it and how flexible/upgradable you want it to be.
If you are willing to invest a little bit of time, Applescript will be much more useful because you will be able to change and improve the program just with a few lines of code. Otherwise you can use Automator and probably have something working within 30 minutes.
What you might want to do is use automator to get the general algorithm down and then write the thing in Applescript, sort of get the best of both worlds.