IMO, the best is the brain shot:

It is less gruesome and quick, and no followup, and you can be ready faster if difficulties develop.

The side brain shot is easier to pull off, in my experience, though others disagree with that.

My near misses on cows have always knocked the cow down, giving enough time for a finisher. I have not had a near miss on bulls but I hear it is less likely that they will be knocked down.

Heart shots always leave a doubt as to whether it is going to fall eventually or run forever.

Get close as you can.