Kobo is generally excellent. Usually if there's a hardware problem, it's visible out of the box, and you can exchange it immediately. Then, you're good for years, usually. The recently available color e-ink screens come with a couple of caveats (no matter what brand reader they are in). The background color is more gray when compared to previous black and white/grayscale e-ink screens (some compare the experience to reading a color newspaper). The second caveat is that at this time, color content renders at a lower dpi than black and white content does on a color/Kaleido e-ink screen.
Thanks! I do not really care about colour screens, but the ability to take notes and write/draw on a monochrome one (with a pressure-sensitive stylus, too) is very enticing.