The Kobo H2O is generally regarded to be the best option if you want a slightly larger screen. Along with the Kindle Voyage it has the best screen (Carta) combined with highest resolution, and good quality inbuilt light, those are the two 'premium' offerings. The Glo HD is a cheaper option and worth trying if you are happier with the standard 6" screen and still great quality screen/resolution just in a cheaper package.
Some people love their Sony T1/2/3 but they don't have as high resolution and carta screen (which are the two things that make the Glo HD & H2O better to read on. They also don't have an inbuilt front light (though not everyone loves this feature and is why they stick with their old Sony), and in addition to all of that, they are no longer supported by Sony.
Whatever you buy to replace your Aura HD, make sure you invest in case for it, and don't leave it in your car overnight.
