In the US, at least from people who post on the diesel truck forums (Duramax specific forums) the 06 and 07 classics (with the LBZ RPO code engine) are highly sought after, Multiple dealers have told me this as well. They are the last pre-emissions Duramax, the horse power went up that year, and they have the 6 speed Allison, which also give you manual shift mode.
I had a hard time finding one when I decided I wanted on earlier this year.
It gets far better fuel economy empty than my 2009 (LMM) Duramax will ever get.
(Yes, I own Duramax trucks)
But, there does come a time when the frustration (and expense) of ownership outweighs the benefits it gives you.