Has nobody started a good chain lubrication thread lately? Synthetic or down isn't really a religious, it's really a matter of choice -- well, maybe it is like choosing a religion.
Having shivered my through a night because of a wet bag, I like synthetic. I'm apparently one of very few people who have trouble keeping a sleeping bag dry. If rain's not splashing in from a downpour, there was heavy condensation on the inside of the tent last night. I don't doubt the theoretical possibility that one can, with careful attention, keep a bag dry during a tour. But my history is such that I'd rather not bet on it, and so I like synthetic bags. If most of my camping were in dry deserts, maybe I'd reconsider.
There's lots of good brands, both for down and for synthetic bags, so any halfway decent outdoor shop will have plenty to choose from. Just stay away from big box crap, and you'll be fine.