I'm a hiker and cook on a camp fire with a canteen cup. So which would be a better material for cooking on a campfire with, aluminum or stainless steel?
Stainless steel. And you do NOT have to ruin the pan on a campfire. Carry some liquid dishwashing liquid (which you will want anyway). BEFORE putting the pan onto the fire, smear some dishwashing liquid on the OUTSIDE of your pan: bottom AND the sides. As the pan sits on the fire, the SOAP will blacken and soot up instead of the pan. When you wash the pan, the soot slips off with the soap you applied beforehand. If you don't coat the outside of your pan with dishwashing liquid, it will soot up and the soot does not wash off.
Stainless steel and as to the soot problem, it isn't. Black absorbs heat faster, so if you let the pan get blackened it will heat up better for you. Most people used cast iron for campfire cooking and it was black and worked well. Trouble with cast iron is it weighs and ton and not good for hiking with.
Direct fire will kind of ruin stainless steel. I've screwed up several stainless steel pans cooking directly on a campfire. I have to agree with wildflower the best route by far in a small cast iron pan. They are pretty heavy though.
I added a few more pieces. Love the glass lids. I have a couple pieces of Le Creuset, but it is too heavy even before the food goes in and I don't like dealing with it. I regret buying the Le Creuset now---should have just bought the Lodge Enameled Cast Iron stuff for about a fourth of the cost. I do have a Lodge 5 qt. dutch oven that I use to deep fry and it is a nice piece and easy to clean. The LC dutch oven does a nice job when I want stew-type recipes.