Kratt is the standard in pitch pipes. They have the highest reputation, so much so that it's hard to name the competion... kind of like, can you think of a harmonica company besides Honer.
The reputation is well deserved. My Kratt pitch pipe has a consistent clean sound that makes it easy to hear the note without a distracting timbre. It has a convienent snap-on attachment that helps play the selected note, which also helps keep the pipe itself clean.