High speed steel or carbon steel.........or maybe something else. Which do you use and why? Thanks, Frank

Powdered steel is probably the best.  Check Thompson tools or Dway tools.  Not sure what steel Carter and son use.  Louie is correct you can get a finer edge on Carbon Steel, however it does not hold an edge very long.  HSS is much better and holds a  pretty good edge and also can be sharpened to a fine edge using white grinding wheels.  Powdered steel holds an edge the longest, however I have found to get a really good edge must use a CBN grinding wheel and they are pricey at abut $150 each but I doubt a hobbyist will wear one out in their lifetime.  They also do not ever get smaller so setting your grinding jig is a onetime deal.
Note Louie's last statement.  HSS comes in a wide array of quality, a lot it has to do with heat treatment.  You generally get what you pay for.

Not positive as I am not a metal head, but when the discussion about which gets sharper comes up, most of the time it seems that the different metal can all be bought pretty close to the same sharpness, but it is easier with the high carbon steels than it is with the M2 or powder metals. Even with the hand plane blades, the old ones from Japan would have a thinner veneer of hard metal for the cutting edge laminated onto a softer metal for the backing/mass of the blade.

Getting a 600 and 1000 grit wheel for my grinder makes for a much better finish cut tool than the coarser wheels, which are better for roughing cuts.

robo hippy