In my views it is perfectly reasonable to assume you break your oath when sneak attacking someone, even goblins and hobgoblins.
That being said I did try to play a paladin also and I was told once I broke my oath without being told the reason, and I couldn't figure out what I did wrong. So I won't be playing paladin in full release even though I like the class, sadly. If they want the paladin class to be playable (other than oathbreaker) I think there should be a warning on actions and conversation options that leads to breaking the oath.
