Noel is a very Christmassy name to me, which is fitting for a december baby, so it's just an observation. It's not one of my favs. I'm not keen on the sound. NO-EL sounds better to me than NO-əl does (which is already better than NOL).
Oliver is a decent name with a good sound. It's been growing on me; I used to dislike it, but not anymore :) I don't like that I've heard it used so often, but I know popularity doesn't really bother you, so that's not an issue. This is my fav out of these three.
August is a name I like mostly on paper. I like the look of it, but not the sound. the -gust part reminds me of 'disgust'. I'm not really sure how I feel about a december baby being named
August. It doesn't
really matter much I guess... I think this is a very good MN, but I'm not overly enthusiastic about
August as a FN.