Personally I use Kobo..not sure why exactly..except maybe cuz I started using it when I had my Blackberry..and that was all that was available really..and so have continued with it. But I do enjoy it. I only briefly pulled up Google Books and looks like it pretty much is the same thing really..only the font was a little smaller stock than on Kobo..but nothing a setting wouldn't change i'm sure.
If you have a kindle no reason to use Aldiko. It doesn't support mobi. format as far as i know. I still rather read a book on my kindle over my phone. But the back lighting of the phone come in handy on occasion. If the new nook would have been out when I bought my kindle I would be a nook owner instead of kindle due to the support of epub. But suppsidly kindle will support epub. at some point in the near future.
Kindle for me. Although I will concede that it's mainly because I have had a Kindle device since it first released 4 years ago, have a large library of books purchased from Amazon, and now carry a K3 which gets a lot of use. So for me to use anything else would be crazy.
It's been a while since I've taken other ebook apps for a test-drive, but the last time I did, Kindle wasn't lacking in any features and their Whispersync services gave Kindle an advantage. I don't know if today Google or Nook offers similar services like Whispersync (last page read sync, sharing notes/hi-lites, etc..)
IMHO, the only downside to Kindle is that it only supports one ebook format. However, if you're like me and only purchase books legally, then it's a non-issue since it's extremely rare a book I want isn't available in Kindle/Mobi format (not a judgement statement, I'm just too lazy to find music/books from other avenues anymore).
