Greg Doss from Wyeast presented an experiment at the NHC last year which showed that 153F was the mash temp that led to the most fermentable wort. My only question with his experiment setup was that the mashes were all conducted for a standard time. If the lower temperature mashes were held for a longer time, I still wonder if they would have surpassed the fermentability of the 153F mash.
Personally. I shoot for 153 for the majority of my beers. I'll go as low as 147-148 for really big beers that I want to ferment down as far as I can get them. For session beers I mash in the 160-162F range to leave enough dextrins behind. If I had a beer that I was rebrewing a bunch of times I might try to dial in a specific mash temp, but normally I don't see enough of a difference between 153 and 156ish where I'd bother with that small of a difference in mash temp. I generally try to dial in the other parts of the recipe first before I start with mash temp unless it is grossly off.
FWIW, Lagunitas mashes the majority of their beers at 160F, so it's not like a mash temp in this range means you're doomed to be drinking malt syrup. A lot of brewers seem to have this idea that mash temps above the mid 150's are way too high, but I just don't find that to be the case in my experience.
or rather +162. I like that mash temp for session beers a lot. Even at modest gravities (1.035~) and minimal crystal additions (<.5 lbs/5gallon) you can get a ton of malt character but it's still plenty drinkable.
And with a really big beer like a barley wine or IIPA mash at 148, add simple sugars and you will still have plenty of body to support lots of hops.