AFAIK the original was copper, they may have made some aluminum versions that i missed before the clones started rolling out/the stuff hit the fan.
Personally i would never buy a mech mod with an aluminum topcap, the threads just wont last.
Regarding continuity obv the copper will be best followed by the aluminum then the steel versions, regarding maintenance the steel version is probably best as the copper will patina(and smell), and aluminum is soft. Honestly i don't love copper topcaps either, but whatever.
How about the black carbon wrapped copper FU hattan that 101vape just got in?