Even though the DS18b20 is a comparative power hog, and it can take up to 750ms (!) to take a temperature measurement, what I do like about it is the packaging: 3 long legs let you suspend it in the air, where it can be more attuned to rapid changes without the thermal mass of the main board (especially if encased in epoxy) creating latency and an averaging of fluctuating temperatures. So, even though it's stated accuracy is +- 0.5C, in a real sense it may offer a more accurate reading of current temperatures than higher accuracy surface mounted temp chips.
So, it would seem there just isn't a single, obviously "best" solution to incorporate into a general purpose platform. For that reason, I think I'm trending toward a hybrid, which will avail itself to different trade-offs to fit different circumstances. The MCP1640 boost converter is pretty cheap ($0.57 on Digikey), and so a DS18b20 could be powered at 3.3v on-demand at any time, even if running from just a couple AA batteries. Seems a bit unwieldy though, unless other sensors might (probably?) also need 3.3v and so could leverage it.