Just to mix up Eduardo ideas a little more.
I was in France lately and got my eyes on a Lafayette. These bags are INCREDIBLE.Craftmanship and desing is second to none. Its on my list as the next to own sleeping bag.
I presently own a Marmot Helium, wich is OK, but I have lost about 20% of loft over the years (the bag is 5 years old)althougth I took extreme care of it (washing, storing, etc.).
I also have a WM Antelope, wich is a great bag. It looks more home made than the Marmot but the quality is much higher. This bag as seen a lot of action lately and is still in perfect condition.
Finaly I am a proud owner of a masterpiece, a Integral Desing XPD3 Endurance bag. This bag was custom made for me (material,lenght and profile (shoulder, hip and foot grit))for my last year expedition to Denali and Logan. ID bags are probably the best kept secrets in the industry. Craftmanship is of prime level,Loft is unreal and custom options endless. Also because you buy in Canada I think they are a cheaper. ID actually dont really like to sell their Down bag because they realy dont make money out of them because of the time they take to built them. (as they say). Incredible enough, it was the first time I had a bag that was almost too warm (particulary on Denali where june was unusualy warm).
As said in past posts, I also think that whatever you select WM, FF or even ID, you cant be wrong.
Althoug big companies states that they use the best possible material, there is not doubt, by the feel of the bag and the way it lofts (even considering the amount of down in each bag), that the down in my WM and my ID is of much better quality than my Marmot.
Sorry for bad, broken english...I am one of those french canadian!