As AZImortal said but in practice there are MANY pal DVD Players that still have problems with MP2 audio. So for guarenteed hassle free playback, AC3 is the way to go. But if MP2 works for you, stay with it, just dont expect them to play if you lend them to your the family or friends.
I just updated my Audio to AC3 tutorial (last week), so check it out and try the freeware ffMPEG, its very simple to use & quite quick as well.