It would be a close battle but Sonic would inevitably rise triumphant.
Firstly, Shadow was artificially built to be Sonic, which means they could both do the same things. Since Shadow was made to be Sonic, that would mean that all the abilities that Shadow displayed were Sonic's. Sonic was always able to use Chaos abilities from the very beginning, he just didn't know that he could.
Furthermore, Sonic was able to sustain his Super form while Shadow couldn't. Because Sonic is the original. What that says to me is that Sonic is better than Shadow in everything. In speed, strength, Chaos abilities, precision, defence, and well, in Super Forms.
All this is to say that I totally agree.