Dale, you sort of opened a can of worms here. Everyone has their favorites for steel, all for good, bad, and indifferent reasons. All that you have mentioned would have their proponents. Some claim that O-1 can be a little fussy when it comes to forging in that it can be a little red short. That is it will mush up and fall appart if it is worked too hot. There has also been some problems noted with heat treating 1095. The W1, 1084, and 5160 are pretty easy to forge and heat treat. I would also like to add 9260 to that list. It is a high silicon steel that seems to hold a edge well and heat treats easily.
With all respect to Jerry, I would recommend that you avoid rebar. Some will harden quite well, like a 6' length of 1" rebar that I found in my back yard when I moved in. Some doesn't have enough carbon to hold an edge. It is all probably from some steel in the 10XX series. The problem is that you will have to test each piece of rebar to determine if it is suitable for knife making and then determine the best heat treatment for it. Leave the mystery metal alone until you have some knife making experience under your belt. You will have enough to learn without having to figure out the heat treatment for each individual piece of steel that you get.
Doug Lester