I have a bike 10sp (4600) Tiagra and think it shifts every bit as good as 5700/6700 105 and Ultegra. I test rode a bike with 2013 9sp Sora as wasn't impressed at all with the shift quality. I also rented a bike with the old thumb shifter Sora and was equally unimpressed. It really comes down to what your expectations are.

BTW, why is the thumb shifter brilliant on Campagnolo but awful on Sora ?