Chocolate to use for Buche de Noel
I like Lindt. I find the flavor very good, and it is almost always available in the supermarket. I use Lindt dark and milk chocolate all the time when I make desserts. The milk chocolate a particular temptation for me, so I only buy it if I am going to cook with it. Otherwise, I'd consume all of it within days.
When I make the buche de noel, I like to do a whipped chocolate ganache filling, so that the whole cake is chocolate through-and-through. I prefer a sweeter whipped ganache than what Beranbaum calls out for in her recipe, so I usually replace about 1/3 of the dark chocolate with milk chocolate. To my taste, this is the right amount of sweetness.
My Saveur recipe calls for semisweet choc. for the icing and filling, whereas bittersweet is used for the roulade (cake part).
No specific brand is called for; however, as usual, the better quality product you start out w/ the better the result IMO. I couldn't personally justify or afford using all Valrhona, so I believe I just used Ghirardelli choc. chips in my case. It still tasted good to me, but I'm sure the Valrhona would have sent me over the edge...
My general rule, based on personal preference, local availability, and price, is Callebaut for milk and white chocolates, El Rey for dark.
On a related topic, I had one of the El Rey single-origin chocolate bars this weekend (don't remember the name) and it was fantastic. There was a strong citrus fruitiness to it - I am planning to save up enough money to buy some for making an orange/chocolate torte.