[soulfuldog]

As they all use Adobe DRM I'd imagine its the same process to get your books from all those shops so none are any less "painful"?

I bought one book from WH Smith a long time ago pre-Kobo (and can't remember what I did with it anyway!), but more recently, when I bought epubs from Books On Board my process was to buy the book, click on the .acsm file to load it into Adobe Reader, locate the .epub file in My Digital Editions and then load it into Calibre.

I *think* they will all be the same. Though Nook is different, I'd avoid them if I were you, and just be careful you don't get the kepub version of a book from Kobo (though I think it's fairly obvious what version you are getting, Kobo users will be able to tell you more).

However, I think your logic on buying epubs instead of Kindle format is flawed. As others have advised, buy on price, not some idea that epubs are better and you are supporting the development of epub (its only better in terms of it being an open format, and if you own a Kindle, that is a pointless benefit, and you are only supporting the shop you buy from, not the development of the format).