Personally, I have used the Glo and Aura HD to view manga and the Aura HD is much better viewing experience. On the 6" eReader I found on some panels are too small to read.
If you are planning to go with the Glo HD you have a few options available:
- Unofficially upgrade internal memory with a larger SD card.
- Store your comics in Calibre.
- Use Kobo cloud storage for books bought on the Kobo site.
- Use Kobo desktop to save your Kobo books locally.