If you want to tow, cubic inches are the way to go. A turbo (originally) was designed to be used as an acceleration tool, and not for continuous use (like towing 3/5k). I'd think you'd want a 4.0 for the low end torque to get you going. Plus, the turbo came on stick trans, and you'd be replacing the trans every time you turned around if you stuck a turbo in front of an A4LD (or any other trans expecting 2.3/2.5 torque output). The blocks are all the same, the mains and rods vary over time, and the holes bored differ based on ignition system used.
To reiterate, don't turbo a base 2.3 unless you are going to use it very sparingly, and that is not the case for towing...
tom