the 105 drivetrain is better if you compare the same years' products. A bit lighter, closer tolerances but other than that, almost undistinguishable from each other to the casual user.
If there is more than a few years difference in date of Manufacture, the difference is insignificant or maybe even in the favour of SORA.

Is the 105 group 8 speed or 9?
I'd say switch it over if it's 9 spd.