Judging from the way the battle went and the conditions it followed it would be logical to assume Danzo was the stronger person, but the conditions favored Sasuke. At the beginning of the battle Danzo was incapable of using Shisui's eye due to using the mind control ability at the Kage summit. This is a HUGE disadvantage. Its never been hinted that Danzo could use the eyes in his arm for sight, so not being able to use Shisui's eye takes away all the advantages the sharingan brings to the table. Not to mention it was shown that Danzo was quite skilled with the sharingan.
Then you have to account for the fact that it wasn't Sasuke, but Karin who discovered the secret of Izanagi. This was important to Sasuke winning as it let him devise a plan on how to defeat Danzo.
Last but not least at the end of the fight Sasuke was practically out of chakra. Had he not taken a bite out of Karin and regained his strength, theres a good chance that Danzo could have still won after being stabbed and losing the shodaime enhanced arm due to regaining the use of Shisui's eye.
Even Madara says "Even though he couldn't use Shisui's eyes. . .you did good in defeating Danzo. . .Sasuke" hinting at the fact that the lack of Shisui's eye was a big problem for Danzo.
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So given all of that, I think its pretty clear that if Danzo and Sasuke had met at random by themselves and fought, Danzo would have won the battle.