A couple of comments:
(1) There isn't a "stock answer" to this question. The appropriate degree of saturation depends very much on the image and on what you the photographer wish to convey. Sometimes higher saturation is more effective than lower saturation, sometimes the reverse, depending on the mood you want. You will observe however, that as you increase saturation, you are merging levels of colour tonality and that supresses tonal gradation which in turn suppresses detail - it's a trade-off you need to be mindful of every time you hit the saturation slider. In that regard, as a subsidiary point on technique, I would suggest first using Vibrance (if you have Lightroom 2.x or Photoshop CS4, because it is a kinder and gentler form of saturation - it provides reduced impact on already saturated colours and larger impact on less saturated colours).
(2) In these illustrations, at least on my properly colour-managed display, the differences between the images within each pair are not significant.