I also was between Kindle Voyage and Kobo H2O, specially I own Kobo Aura, and I like their software, and pocket integration. Where I live, there is a Fnac shop that sell Kobo H2O, so I checked it and it's amazing, light and screen size.
I received my Kindle Voyage yesterday, and I can see that it has wonderful screen, but there is this an even pinkish color that show up and disappear based on lighting around me.
Still, I'm going to keep the Voyage, H2O seemed slow for me, the screen sometimes just not responsive compared to the Voyage, the Voyage is snappier and the "Page Flip" feature is a blessing.
Kobo software has become more stable than before, and the quality of build is good, I didn't have Voyage and H2O next to each other, but I did play a little bit with H2O and I think the text is crisp, probably with the right font and setting you wouldn't notice a difference between Voyage and H2O.
Still, the Voyage font seems to be as perfect in darkness and in look as I would dream my perfect reader would be, if it wasn't for that pinkish tone :/
Kindle Voyage stay, hope for Kindle Voyage 6.8" or even 8"
One last note, I tried Kindle Voyage with PDFs, and it's just amazing and snappy, I don't think it's the same case with H2O, not with my few visits trying normal kepub books, I'm not sure if it's because of the infrared screen.
You would love both, just keep in mind it's the book not the paper ;D
Well, the paper a little