I myself prefer down. I have one synthetic bag which really only lasted five years before it went from being a 20F bag to a 50F bag. My other bags are all down, and the favorite among them is a Western Mountaineering Megalite that is about 8 years old but which I still consider "new" despite very extensive use (guessing well over 1000 nights). At 30F, though, it's a bit light for a lot of what I do, so I'm currently shopping for a new bag for an upcoming tour. Since I'm going to be at higher elevations the whole time I'm going for 15F. Note that the rating on bags is basically whatever the manufacturer wants to say. Usually it's something fairly close to the EN rating for men, but not always.
For example, I really like the Marmot Helium. It's rated 15F and has an EN "comfort" level of 16F for men, 28F for women. I'm a cold sleeper, so I split the difference between the two, meaning for me it's probably a 22F bag. REI gives EN numbers for many of the bags they sell, but not all bags are tested in this way.
On the whole down vs. synthetic debate... well, I just haven't used synthetic bags extensively in the last 15 years and while they obviously have come along way every time I shop for a new bag I end up finding I can get a warmer bag for much less weight, so even though I know it's gonna cost, it will also last way longer.
In my searching I've found some great deals right now on a couple of good down bags through REI outlet:
REI Mojave 15F $118
REI Sub Kilo 20F $159.93
I'm seriously thinking about the Mojave, 'cause that price is hard to ignore. But it's not on par with the Marmots in terms of quality of construction.
You might find this
Sleeping Bag Comparison Matrix helpful as well.
Edit: in response to markf's comment
they are hard to clean without destroying the down. This is completely not true. Get a bottle of NikWax down wash and either find a front-loading washing machine or throw it in a bathtub. I usually put it in the spin cycle of either style washing machine, then in any dryer with some tennis balls on medium heat. I've washed my down bags many times, and they are always the better for it.