Why I like Kobo over Kindle and Nook (even though Nook wasn't asked about
)
1) Font control. Kobo offers -far- more control than either Nook or Kindle, you can change the size, weight, line spacing, margins, etc. all with more options than either of the other brands. And you can load your own font on the device without any fuss.
2) Bigger screen, I got the H2O because of the 6.8" screen. With tweaks and patches the readable page gets close to, if not actually more than, what is on most mass market pages.
3) Calibre, Kobo just ties in so nicely with third party software. It's like the execs thought 'Hey, we can save money by not trying to exclude third party software from interacting with this device, and then we don't need to worry about making a feature rich desktop app, if we leave this open. So yes the Kobo desktop app may not be the best thing in the market, but I'd rather they spend the money/time improving the reader software rather than the desktop software.
4) Less ties to a single company. I understand you can get ebooks purchased from other places on a Kindle, but from what I have heard it's a more involved process than either using Calibre or drag/droping the files onto the device. The eink nooks are easy to load things on to, but given the direction BN has taken with their tablet line, where side loaded content is treated as a third class citizen, I just don't want to be caught if/when BN moves in this direction with eink. Their Glowlight Plus actually does make things a bit more difficult to load.
5) User customization, Kobo hasn't locked down their devices unlike both BN and Amazon. And while you can root the Kindle and Nook, it's just so much easier not to have to deal with it.