For the health benefits, without some of the downsides, I believe it is preferable to drink coffee when you are not tired. This way you don't get a crash later, because there is no adenosine build-up (the 'tiredness' signaling molecule that caffeine blocks). I believe this also helps to prevent addiction, because there is also no up-regulation of adenosine receptors.

This works great if you drink coffee for the taste, rather than as a way to stay awake (which works in a pinch but is counter-productive over the long term).