"I would stick with down if at all possible because they give you much more value than even the best synthetics. Down bags compress smaller, last significantly longer, are far more comfortable, but are more expensive."

Far more comfortable? (huh?) Value? Synthetics are generally cheaper for those with similar levels of quality and warmth. The top synthetics (i.e. Primaloft) will resist moisture much better than Down and will continue to insulate at least some degree if wet - down won't. For those who say that their down bag never gets wet, they are wrong. Everytime we sleep we emit about 1.5L of moisture over a 7 hour period - more if we are sweating to any great degree. Every down bag will absorb this moisture and lose some of its loft and hence ability to retain heat until it can be dried out, which may or may not be possible on the trail. This is not the case with the top synthetics. Synthetics will also resist loft breakdown over time due to compression - down bags will not. Down bags will last longer if taken care of but they also tend to be fragile.

However, synthetics will be heavier than their down competitors, apples to apples, with similar temp ratings.