Are you a tuner? Will you be modding your car?
If you aren't or don't plan on going all out, stick with the V6, it will be more instantaneously rewarding. There are also a few mods out there that can easily give you a decent wallop for your buck. Thing that comes to mind the most is a modified ecu chip that could net up to 20 horsepower and twice as much torque.
The 1.8t engine has been around forever and most tuners have gotten the engine into the 300 horsepower range by replacing restrictive parts like the manifold and small turbo. modified ecu chips for the 1.8t can give you like 40 horsepower and 60+ torque. It can get expensive and time consuming to do so much work.
Again, this is just from a tuner perspective. If i were going to convince someone on the street that doesn't seem like he knows about cars... i'd just say get the V6 cuz it has a six speed... and six speeds are FUN.
