Let's not forget that multi-step mashes are an option, too. If you think about it, it can afford you a greater control over your wort fermentability in the case that you are uncertain if the entire mash has a uniform temperature during a single-infusion mash. Matt Brynildson at Firestone Walker uses a separate beta and alpha rest for many of his beers, and I sure trust that guy!
I recently did a Belgian Blonde which I mashed in the upper protein range (132F) for 15 minutes, then 147F for 40 minutes (shorter than a single-infusion beta rest would ideally be, as others have mentioned above), and then 40 minutes at 156F to finish the conversion with some less-fermentable sugars. I've just packaged/carbonated the beer and it has a very firm-yet-refreshing medium body, even with having used 8% cane sugar. But everyone's system is unique, of course.
For single infusion mashes, the general rule seems to be that if you're doing a pretty high gravity beer (> 1.075 or so) that you do not want to have an overly sweet/big body (i.e. it's not a barleywine or Imperial stout), mash low -- in the high 140s or so. If you are brewing a low gravity session beer and want to avoid it becoming too thin, mash into the mid 150s.
Of course yeast strain choice plays into it as well. And your own system's fermentability (everyones is different!). And your own drinking preference. I like to mash lower than most people but that is just me. It just takes time to find out what works best for your own enjoyment (or for the judges' enjoyment, if that's also a goal).