The Nottingham will be fine. You have to realize that the main difference between a stout and a porter is in the grain bill, not the yeast. I think you'll be really happy with your stout. If you really want to test it out, make the same beer again with one of the other yeasts. Then do it again with another, then another, then another... and so on. You'll find the one that you prefer and then you've got your recipe down (at least yeast-wise).