Depends on what you want to do with the car.

Occational racing at the drag strip or autocross, but you will drive it around all of the time? Then probably the GSX.

Auto tranny will be better for being lazy during commutes. AWD for bad weather. The GSX is better equipped than the RS so it would be more enjoyable for a daily, especially since neither car would be expensive compared to a new or not too old car, so might as well pay a very little more money (again, relatively speaking) for more car. You can still make the car fast without going through too much pain, money, and effort even though auto isn't the best off the line, but if it is mostly a daily it iwll be plenty fast from a roll regardless of tranny, and as a daily it will probably be a better choice.

A race car that is very light? The RS. Car is the lighest 2G already, can be stripped to make even lighter. Not as hard to do as there is less stuff to take out. It will be FWD so traction limited but it's not like people haven't raced FWD with good slicks before. You'd have to build up the engine whether it is a 420A, 4g63, or anything else so you can make the 420a bulletproof.