Ottawa Archer, I've done both and my rate of success is much greater on new, known steel. I dont mean to be smug or spoil your zeal. I strongly suspect that some guys get into knife making thinking it's so cool to make something beautiful and functional from something that is either useless articles of the past, or from something that is sentimental to them. While this is very true, it ups the difficulty factor a lot.
If you want to get your feet wet in making knives, I would like to see you get some successes under your belt using known steels, then have a point of reference to compare the unknown steels with. This does two things. It enables you to have known factors to build your knowledge, and it allows any potential help from an experienced maker to pinpoint a problem for diagnosis.