With the VR conversion you will need the VR box as well as the running gear (Hubs, carriers, shafts, cable shifter etc.), with the 1.8T you can retain all of your running gear but you will need to plum in an intercooler with all the associated pipe work, both require higher pressure fuel pump, ECU's, some form of mapping and exhaust fabrication.
VR is heavy and it sits too far farward in the bay if your after outright balance on handling, power to weight ratio on the wrong side, 1.8T sits pretty neatly just as the standard motor, lighter better scope on handling.
So ultimately the choice is your on your what your after from the conversion, I wouldn't go into the fuel debate as both can be thirsty as each other depending on the state of tune/power, also very dependant on the budget, clips on youtube and the practical of the actual conversion are two very different things, so consider carefully and then select.
PS. R32 conversions sits even further forward in the bay..
