I find Adobe one the easiest to decrypt, because with Adobe DRM I just have to use Calibre and a Calibre plugin and it removes the DRM automatically when I import my book into Calibre, I have nothing more to do
I prefer buying on the Kobo store because this way I have kepub expanded version, and I can download the ADE one as well. So the best of two word, a prettier book with the kepub version, and a DRM free (mmm Adobe DRM then DRM free ^^) version for Calibre as well