Considering Spare Parts, Mechanics & Fuel Quality 2.5TDi or 2.8TDi are the best engines, no sensors, no electrical issues, easy to maintain. Spare parts for V6 are very hard to find.
Considering most travels on motorway & long trips 2.5TDi & 2.8TDi will suit you best. 2.5TDi can give 8-9 Km/ltr in local & 10-12 KM/Ltr in long. 2.8TDi version can give you 7.5-9 Km/Ltr in local & 10-11 Km/Ltr on long. Both engines can go above 120Km/Hr, especially 2.8Tdi can go till 160 KM/Hr.
Hope my points & opinions help you.