I prefer some sort of ebony, but have read the oil in it can be a pain when glueing it.
I use a floating tenon mortised and epoxied into the barrel channel which subtends both the walnut fore end and the ebony tip. That eliminates the dependency on end grain-to-end grain glue joints and guarantees they'll never separate. To get a good bond onto the ebony, always wipe it down with acetone to remove the oily residue. I never had any ebony come loose from anything when that precaution was exercised.
Ebony will also take any finish without any particular prep work.
