The Voyage is meant to be a step up from the Paperwhite, just as the Oasis is the meant to be the premium offering in the Kindle ereader line. I went from a PW2 to the Voyage, and am very happy I did so, the adaptive light, pagepress buttons and most of all, the flush screen where the text seems almost printed on the screen, are the reasons why I like it over the PW.
If dictionaries are important, nothing matches the dictionaries included with the Kindle range, and I think highlighting is a better experience on Kindle's but note taking is probably fairly similar (not something I use). The dictionaries are definitely a huge plus for the Kindle over Kobo, but there are some pros for the Aura H2O over the PW, like the bigger screen and improved font options.
For someone outside of the US, the Nook is not of much interest, even in the US it doesn't fill a gap, it just offers an alternative to the Paperwhite.
