Penalties are always in favor of the penalty taker than the keeper. As a matter of fact, I remember reading/hearing once that the reaction time of the keeper is so slower than the time it takes for the ball to reach the goal line. A penalty is never a 50 vs 50 situation. Regular penalty takers such as Messi and Ronaldo have a tougher job, as they are watched all the time and their penalties are recorded, statistics made out of them, so keepers can have an advantage if they see a certain pattern/algorithm in their penalty taking.
Personally, I like penalties that are taken with a strong shot in the corners, so that even the best keepers don't have a real chance.