Forstner bits.

The big benefit of carbide is its temperature resistance and long wear. Big downsides are that it's relatively difficult to sharpen, doesn't take as fine an edge as steel, and is relatively brittle.

Unless I knew in advance that I was going to be doing high volume or working wth some of the hard and abrasive exotics I'd go with HSS.

Personally I've got an old Chinese-made carbon steel set that has drilled everything I've thrown at it and never given me a problem, but I almost always use the drill press and adhere to the speeds marked inside the top of the box lid--they work fine in the hand-held drill but generally if I need Forstner precision I want the precise positioning I can get with the drill press.