What makes the best material for valve guides and why?

Respectful greetings to ye Seasoned Moparian Gearheads! The more I research the matter of refurbishing cast iron heads, the greater my self confidence grows toward making the effort at home, except for a sonograph, magnaflux hot bath and if necessary minimal planing the mating surface with the cylinder block. Getting my two Little Darwinian Imps into some educational institutions should free me to do MUCH of the more menial, time consuming tasks in my Shade-cactus barrio hovel workshop....

What makes the best material for valve guides and why?