I never said I know what sounds best - I said I know what sounds good. When I'm practicing stuff I have played before, I'm finding other things that also sound good. I play church gigs, which are ad hoc bands - all good musicians, but every gig is different. I end up playing with different musicians, different singers, with different arrangements, in different keys, with different audiences, etc. If I play the exact same part 3 weekends in a row, at least 2 of those are not optimal. Having a lot of places I can go means, when the vibe isn't what it was last time, I know where to go to make it sound really good this time - which is different than last time. Or the time before that, or....
The short answer is there is no "best" that applies every time you play a tune. You figure out "best" for a particular gig from a bag of "good" possibilities - in the moment. Practicing makes your bag bigger.