I used to purchase my manga from Nook, then switched to Amazon and now have gone to Kobo. The switch was pretty much based on what platform is easiest to remove DRM from while providing the highest available image quality.
I typically just convert to cbz and read on my iPad (ComicGlass) but have recently started reading manga on the Kindle PW 3. Caveat - it's a hassle to convert from kepub to mobi/azw3. Calibre's output doesn't display the image fullscreen while KCC can be overly aggressive at cropping margins. I'm starting to look into getting a dedicated Kobo reader for reading Kobo purchased manga.
The Kobo Aura is a non-starter given its low resolution/pixel density. The 32GB Kobo Aura ONE Limited is a bit pricier and bigger than I'd like, not too mention I actually do like raised bezels. Kobo Aura H2O (1st ed with microSD slot) is under consideration but it's just a wee bit on the heavy side for my taste (RSI).
I saw Kobo Glo HD manufacturer refurbs for $90 on ebay and came across a post with instructions on upgrading the internal SD card (already have 32-64GB Samsung microSD cards on hand). Do you guys think it's a good option at that price for my target usage? Also, what's the max storage it will accept? I'm considering springing for a
128GB microSD.