First few names that come to mind from the pro scene are Walshy, Snakebite, and Bravo. All three are consistently incredibly cool, calm, collected, and positive. And I'm a sucker for Walshy's awesome (terrible) jokes.
From the Twitch/YouTube side, Stress, Vetoed, and ShyWay are the first few I think of. Really chill, great content, and seem like genuinely good dudes.
Obviously, not a comprehensive list, but positive role models in Halo.