[GeoffR]

My favourites would be Baen and some publisher shops such as Spatterlight Press: All their books are DRM-free and without georestrictions, if only it was like that everywhere. Unfortunately not a big range, and nothing from the big publishers.

Otherwise my favourite is whoever has the best price on the day. In New Zealand that is usually Kobo (they charge in New Zealand dollas so no currency conversion or credit card fees, and most books are eligible for promo codes including the majority of the big publisher's books).

I've never had an issue with any retailer's customer service. All my problems have been fixed or a refund offered. (Edit: Although if the problem has to do with book content or availability I think it is better to deal with the publisher direct rather than go through the retailer.)