Lions are pack hunters, they are not stupid, they know that the kick or gore of a bull causes then an injury that will result in death. They would not even attempt this unless it was a dire situation. Even then just like any other fight it would be which ever party used their skills best and gained control and took advantage of their situation. The will to survive is stronger than the will to kill so this gives the bull a huge advantage. If the lion fails they will get to live and try another day, the bull does not.

My money is on the bull 90% of the time

I would think it depends entirely on the bull's first charge. Hitting the lion with it's horns full speed would be devastating for the lion. If the lion were to evade though, the bull's momentum would keep it running long enough for the lion to give chase and in that situation, the lion would easily catch up to the bull and jump on the bull's back, stick it's claws into the bull's sides and sink it's teeth into the bull's neck. No matter how big the bull, the lion would drag it down eventually.

So, it all depends on if you think the bull is more accurate than the lion is evasive and from that, you have your answer

The lion. Lions eat bulls all the time.

A single lion would not be able to bring a Bull down on its own. In African Documentary it shows it takes at least two lion s to bring a wildebeast down, which is slighter Bigger than a bull.

The one with the bigger teeth.

Lion. Speed kills. And Lions are faster and more nimble.