As most have said, the set-up will affect how well it shifts more than the actual shifter/derailleurs. I'd even suggest good internal and external cables on Tiagra/Sora that are maintained well would be a lot smoother than DA that is left to rot in the garage.

But then again, I have only ridden DA twice, Ultegra once and Sora is on my own bike (upgraded to STI shifters this year). I have to believe Sora is just as good in performance, I can hardly afford 105/ultegra, nevermind justify buying it.