Always in a glass.
For head purposes, my default is the same as with any beer, basically the 1/3 - 2/3 rule described above. However, once I get to know a beer, I may modify that. For a lightly carbed beer, which most of mine have been, a brief splash in the bottom first helps get the CO2 release going.
For sediment prevention, I pour until I see sediment approaching the end of the bottle, then stop. I take care to limit the amount of sediment that goes into the bottles, so often this is 1/4 inch or so. With dark beers, I don't worry about it at all. There's yet to be enough sediment to have any significant impact on the taste. The only exception was in a batch of hard cider, where the yeast gave it a pronounced flavor, maybe diacetyl-ish, I don't recall exactly. It wasn't a bad flavor, it was a pleasant alternative to the dryness that came when there was no sediment, but it clouded up the otherwise crystal clear cider.
As for the excess left in the bottle, come on guys. Whether it's 1/4 inch or 1 inch, just drink it out of the bottle. No waste of beer, no waste of B-vitamins, and no cloudy beer. (As I said, though, I have had very good control over the sediment, so it's really just been yeast which is not unpalatable; I've had some homebrews that clearly had some actual trub proteins in the bottom... I'm more hesitant to drink that.)