On a case-by-case basis :) Unfortunately, it's not just the two of them. In general, I always start with simplest ("most readable" in the sense of easiest to

On a case-by-case basis :) Unfortunately, it's not just the two of them. In general, I always start with simplest ("most readable" in the sense of easiest to understand) implementation that I have the time to implement (time is another variable). If a performant version is a no-brainer in terms of cost to implement, and at worst only slightly reduces readability, I'd probably go with that just because I like to be proud of my code (satisfaction in a job is yet another variable). Ultimately, I rarely find that readability suffers with performant code. Unreadable code is usually non-performant because it is hard to improve. Focus on performance sometimes simply reduces how reusable/generic code is, but I don't find readable and performant to be in opposition at all.