I have the stillen sway bars and I am putting 20 inch rims on wed with 245/275 tires. Which settings should I use that would give be the best handling and less chance of oversteer and understeer.

 

Generally new cars will have a tendency to understeer(push). The G is no different. Stiffening the rear and softening the front sways is one way to make the car more neutral. You might want to start out with med/med as suggested by the Stillen guide or even soft/med front and medium rear.