The Manhattan

Those out there who have strong opinions on such things:

1) I hear different versions of what a Manhattan ought to be made of: rye or bourbon

Back in college I was making them with Jim Beam rye, and the results were so-so. Tonight I tried making one using Marker Mark bourbon. It was pretty darn good. (But then, Markers Mark is pretty darn good...) Which leads to the second question:

2) How good a whiskey needs to go into a Manhattan? Is putting Makers Mark into a Manhattan overkill? I hesitate to have Markers Mark any way but on the rocks -- and yet there's the principle that good mixing requires good ingredients.

When dealing with gin, I use Citadelle or Bombay Safire for martinis (or straight up) but Gordons for Gin and Tonic and Gimlets. Is there a similar hierarchy of bourbons appropriate for different drinks? And if so, what is the appropriate bourbon for a Manhattan?