Destiny Islands has always been my favourite. It hardly ever gets attacked by Heartless or Nobodies, it's beautiful, it's peaceful whilst still having a good community of people and you'd get to hang out with Sora, Riku and Kairi. Plus I want to see what the main island looks like as we've never explored it. Lastly Terra and Aqua indicated that it's a world bathed in warmth and light unlike any other world which makes it sound basically like heaven.