Except for rain, the various modes on our bikes are basically personal preference on throttle response and a gradual lessening of the electronic safety nets. While it is possible, I doubt more than 1% of the riders on this board can push the bike hard enough where the differences between race and slick mode would actually make one "faster" and to ride the bike like this on the street would be suicidal.
So its all about what mode gives you the best feel from the bike and has the level of electronic intervention you are comfortable with. No right/wrong here. I could see that being any of the three main modes depending on the rider and conditions. And in some conditions, maybe even rain (like riding in the rain).