Disclaimer: Yes, this page is pretty light in content for a chocolate website. It was either go live with this or nothing for chocolate as an ingredient. I will expand this page in early 2007.
Brand of Chocolate
There are a lot of chocolates out there. If you have a favorite, see of you can find it in bulk blocks-buying 4 pounds of chocolate in 6 oz. bars will not be cheap.
Dark or Light
This question is not like the Pepsi challenge—there is more than just taste going on here. Dark chocolate has more cocoa solids and tempers at a higher temperature than milk or white chocolate (which has no cocoa solids, just cocoa butter). Still, it all comes down to what you like. I prefer dark chocolate—the higher the percentage of cocoa solids the better, but anything beyond 75% is getting a bit too bitter for just about anyone, which is why you will rarely see anything above 74% that is not "baker's" chocolate (100%).
Whichever you choose, just keep in mind that because white chocolate contains no cocoa solids, you can't readily swap it with milk or dark in recipes outside of dipping. Unless you are experimenting, don't substitute white chocolate for milk chocolate in your ganache filling for your truffles. Finally, keep in mind milk and white chocolate require lower temperatures for tempering.
Flavor is important, but workability also varies with each chocolate, even those of the same brand. Some chocolates may thicken quickly than others after dipping a dozen cooled truffle centers. Chopping chocolate can be a messy affair, with bits of chocolate flying across the room.
There are special tools for breaking up chocolate, but some chocolate brands are available already broken up into small discs and this can save you prep and cleanup time. It is definitely more convenient to just toss in a few more discs when weighing or tempering. If you are tempering without a machine, you might be better off with a block which you can shave into smaller pieces with a serrated knife.