In the hands of a more power shinobi,the sharingan is better than the byakugan
Trying to compare the two is like comparing apples and oranges, as many people have already tried to state!

The byakugan and the sharingan are designed to do two completely different things, and as such neither is really 'stronger' than the other. The strength would depend on the INDIVIDUAL shinobi's strength. In much the same way, Neji is stronger than Hinata but we don't really have any way of comparing Neji's strength to Sasuke's.

Would Itachi beat Hyuga Hiashi? No way of knowing. Without having seen anything in cannon to give us a base to go by, we could debate this issue to death and never get anywhere.

Final answer: Neither the byakugan or the sharingan is 'stronger.'