I would choose Noosa Heads or Noosaville anytime over Byron. Noosa has the best lifestyle hands down. I've lived here 12 years. Have visited Byron and very happy to come home. Much more real, relaxed and friendly in Noosa. Real sense of community.
I would definitely pick Noosa over Byron. Bryon is a lovely place to stay, but the climate is a little bit warmer in Noosa and it still has a relaxed and casual feel to it, even when it's holiday time. I've found Byron to be far busier during Christmas and New year. There's always a great mix of people in Noosa and they're generally quite friendly.
Byron is a great spot and well worth the visit however I would choose Noosa for a longer stay because there is a lot more to do around the Noosa area if you were on a longer stay. Geography wise, Noosa offers a lot more as it has not only the beaches but also the salt water lake and river system to explore.
I love visiting both Noosa and Byron. I still believe the best kept secret in Australia is Bribie Island. The only off shore bridged Island on the East coast of Australia. Though a holiday home in both Byron and Noosa would be just fine.