If it's fuel economy your after any VW engined diesel will fit the bill but not the 1.6 tdi as I've never heard a good word about them from anyone that owns them, the GTD is the range topping golf diesel but I think the GT TDI offers better value really but the GTD seems more sought after used.
The 2.0 CR TDI is also very quiet, if not the quietest I've ever heard for an oil burner and the engine pulls strong and hard in all gears.
Driven slowly I can get amazing mpg, driven normally with some thrashing I see 50 mpg and if I "go fast" I never see below 40 mpg on the route I drive.
All in all it's like all modern VW's, it's a good car, but not a great car, I'll be going back to a BMW next I think as my last car, a BMW 535d was a great car indeed and I had no faults or problems with it apart from the optional 19" wheels cracking.....
I'd suggest driving a BMW 123d or an BMW Alpina D3 with the 2.0 Bi-turbo diesel engine before buying another VW.