I prefer copper. Not because I can tell a difference or anything, I just have a thing for copper and it's natural beauty. Stainless steel is boring, it doesn't patina or age. Brass is nice too I guess but I like copper better. Right now I have a jux mod and tactical warhead rda and it's a very nice setup all in copper. But yeah can't really tell a difference in different metal materials really when comparing the same mod in different materials. However you can tell a difference between mods even if they're the same material. Copper vanilla compared to jux mod. There's a noticeable difference between the two