Which of these locations in Queensland might be the best to live in?

Native QUeenslander here: out of those three, I'd go for MOoloolaba for sure. It's only about 80 minutes drive on freeway into Brisbane city itself for arty, cultural stuff and/or partying! Plenty of pretty seaside landscape and also pretty inland areas, with Mooloolaba or somewhere similar for your main accommodation. All of the Sunshine Coast areas would be nice - check out Caloudra shire (I think) and Maroochy shire. Lots to offer for nature lovers. Hervey Bay is pretty - is the take-off point for Fraser Island (awesome for campers etc), however nightlife in Hervey Bay or Bundaberg would be extremely limited. Try further south, I'd say, like the Sunshine Coast. It would have to be easier to get a job in Mooloolaba/Sunny Coast than the other two as well, I'd think - far more populous.