Age and mileage wise, a GTD is going to cost a whole heap of more money to buy. Personally I think the best all rounder in the range is the GT TDI. You get reasonable performance, near Bluemotion fuel consumption and lots and lots to choose from, meaning you can be sure of finding a good one. Also, there will always be a strong market for diesel engined Golfs, so it will still retain a strong residual.