Sway bars really can't or shouldn't be considered alone. They work side by side with spring rates and tires. Handling is the sum of all parts. You can consider upgrading in steps according to your feel for what you want but that may or may not be the "best" or even an improvement.
I am sensitive to feel in the steering wheel the soft rubber used in the front control arm bushings lacked feel for me. I also changed to wider and shorter side wall tires. Stiffer springs solved the sway issue and much better shocks solved the damping issues. A slight increase in rear sway bar size decreased under steer so that now I am happy.
Right now I have KONI STRT + STEEDA Sport Springs, wider rear Michelin Super Sport tires 275/40 R19 mounted on 19X9, front ones are the stock 255/40R19 pirellis. Yes I'm planing to track the car, but looking for improvements like sways and watts link