[mgmueller]

I seem to be a tiny minority.
I have my Aura H2O for about 3 weeks.
I've used it maybe 2 hours in total.
I find it inconveniently bulky.

So, my personal verdict, comparing Aura HD, Aura H2O, Paperwhite 2 and Voyage:

a.) Form factor
I wasn't too enthusiastic about Aura HD. Its design somewhat reminded me of a digital watch from Eastern Germany around 1990. To me, it did look a bit dated and somewhat on the ugly side. But if I compare to Aura H2O, I actually prefer Aura HD. Now I've come to value the "fold" on the back of Aura HD. Aura H2O to me, without the fold, simply feels blocky and bulky and slippery to hold.
I've always liked Paperwhites 1 and 2 and now even prefer Voyage. I love the display being even with the bezel. I don't care much about the page turn buttons, though.

b.) Micro SD
At first, I liked the idea of the Micro SD on both Kobos.
Not for sideloading, I'm not spending my time anymore with fumbling around.
But my original libraries from the respective merchants simply are too big: About 1000 books from Amazon, about 350 from Kobo and so on.
One might think, at least the 350 from Kobo should fit into the internal memory. But unfortunately, I've got a few dozen huge travel companions.
I'd rather have my entire library with me, instead of relying on the cloud. So the Micro SD did seem a good idea. But actually, you can't manage it at all. Kobo simply fills the internal memory and then the rest to the SD card. I'd like to decide myself, for example small text books to internal memory and huge travel companions plus Garfield comics to the SD card. I could do so, by manually downloading book by book in the respective order. But even for only 350 books that's a PITA. Why not offer some simple file management in the Kobo OS? Like "download by size" or "click for download to internal memory, unclick for SD card"...

c.) OS & user interface
I consider them on par. Maybe I've missed it on Kobo. But on Kindles I love to add my own dictionaries. Buy them and then define them as the standard. Else, both are quite similar to me.
On Kobo, I love that I can see the size of the files in list view.

d.) Waterproof H2O
I won't need it much, but it actually was my main motivation to go for H2O.
I've killed 3 DECT phones a few years ago with the steam while in the bathtub.
I actually thought about ordering a customized waterproof Paperwhite from some manufacturer in the US, so H2O seems a nice idea.

e.) Customisation
I guess, that's the main reason, why many of you seem to like H2O or Kobo in general.
I've used calibre a few years ago myself. Mainly, to have all books on all readers. But at some point, I simply found it too time consuming. I couldn't stop by just converting the books (back then, I've had about 300 .lit, 300 .lrf, 250 .pdf, 300 .epub, 300 .mobi and maybe some more). Once I touched the books, I've modified metadata, covers and so on. And eventually I found, I barely ever read a book outside of its original reader. So I simply decided, to buy a few books a second or third time and to collect a few readers. Sometimes I was switching to nook Lowlight or Aura HD, mainly I've used Paperwhite 2.
If someone enjoys fumbling around and building his "perfect library", Kobo obviously has some advantages. To me, it doesn't matter anymore.

f.) 3G
To me, that's still one of the killer arguments for each Kindle.
I buy them all (10 so far) with 3G.
I don't want to use another SIM card (I've got 6 already) in a reader. I don't want to bother about WiFi in lots of places (in my standard hotels yes, but not everywhere). But I love, being able to stumble though the book store whenever I want, wherever I am. Having 3G without needing a SIM and without additional costs to me still is a stroke of genius.

g.) Bookstore
I slightly prefer Amazon.
I like the idea of coupons from Kobo, but most of the times they don't work in Germany. Probably due to the unique (dated?) book-price binding we have.
I hate B&N, I really don't want to use VPN so some merchant is friendly enough to take my money. So Kobo is my second choice, but for whatever reason still ranks behind Amazon.

h.) Display
Many (most?) of you would rate display first or at least amongst the top 3 issues. Honestly, I seem to be less critical in that area. Maybe because I've started reading eBooks in 2000 on Pocket PCs and never had a problem then either. I'm perfectly fine with all my readers. I still like my old Nook classic, which doesn't even have a Pearl screen.
Nowadays, I simply prefer Nook Glowlight, Kindle Voyage (Paperwhite 2 before that) and Kobo Aura H2O (Aura HD before that) because of the light. I've re-discovered reading in bed for 2 hours because of that great feature.
Without that, I even would be fine with my Sony 505 (which btw in my opinion still is one of the most beautifully designed readers I've ever seen).

i.) Size
I find Aura H2O too bulky and don't enjoy holding it much. But frankly, Kindle Voyage could be bigger. I'm fine with the size. But it's that compact (small bezel and such), it easily could be 1" or 2" bigger without being bulky.
I very much prefer holding Voyage over H2O. Due to the bulkiness of H2O and due to the elegant styling of Voyage. But I wouldn't mind, if Voyage would be a bit taller.

j.) Design
I find Voyage beautiful. The bezel having no gaps and being even with the housing: Absolutely great. That's the main reason for me, why Nook Lowlight ranks relatively low: The build quality (gaps in the housing) is a mild disaster. H2O is okay, but Voyage in that regard is miles ahead (for me).

k.) Customer Service
Some have mentioned customer service/support as a potential hurdle against Kobo.
I've been pissed about Kobo about 2 years ago. I did receive a book with corrupted cover and (at first) Kobo customer service did refuse a refund. One never has to discuss with Amazon, you get a refund "no questions asked".
But then, in mobileread, in my thread where I stated my frustration about Kobo, 2 employees from Kobo jumped in. And one of them actually did solve my problem and manually added the correct cover to the webstore.
So: Amazon customer service certainly is great, maybe even benchmark. But they, like most (almost all) other customer services, are reactive. Responsive, customer friendly and fast - but reactive. Kobo, in my special case, has been pro-active. I wouldn't expect that and it certainly remains the exception. But sometimes the "underdog" actually might be more responsive than the market leader and might go the extra mile for you.
Personally, I don't focus much on customer care. I assume, the new gadget will work flawlessly and I'll never need customer service. But in this case, I wouldn't worry about Kobo.

My simple summary:
Many of you probably are into customization and calibre and the likes.
And that's probably the reason for ranking Kobos relatively high.
I don't bother about those things anymore, I want to start reading as quickly as possible and never again bother about anything else.
And then, regarding convenience, bookstore, design and such, I clearly prefer Voyage.