Tiptronic or Manual?
A good question. We tow an Eriba Triton (MPTLM 1200kg) and previously I had a Golf TDI 130 with the 6-ratio manual box - no problems - aside from extra care with hill starts - and relatively good fuel consumption towing (35mpg to 40mpg).
We now have a MB C270 CDI with the 5-speed automatic gearbox, and it is so much easier - perhaps relaxing is the best description - to drive. Fuel consumption towing is around 30mpg to 33mpg.
Towing our Eriba on a motorway, both cars would run happily at 55mph to 60mph in top gear - engine revs around 1800 rpm - so the engine is developing maximum torque.
If you drive a bit slower, then the autobox may change down one ratio (to stay close to max. torque) and you can find yourself going slower and using a bit more fuel.
Suggestions:
Test drive the automatic and if you find not having to change gears relaxing, then go for it.
If you have a choice, a very useful option on the Passat Estate is the self levelling suspension - this is a big help when towing with front wheel drive.
So a Passat TDI 130 / tiptronic / self levelling suspension would be my "ideal"
Robert