Copper can look nice as it ages, it gains some character. I am not a fan of the smell or color it can end up leaving on your hands. Hold a penny in your palm for about 15 minutes and check the smell. I worked with copper on some projects and the odor kills me now. It also tints my skin slightly green. I can smell brass as well but it does not bother me in the same way. We tried sealing a friends copper mod with Collinite 845 and it did not work to keep his hands from getting the stain. Maybe more or different coats would work. Either material has greater conductivity than stainless though though copper is much softer and can get dinged up with wedding rings etc.
I have both copper and brass. Copper is a high maintenance material. Needs to be cleaned every couple days to keep threading and parts clear of tarnish. Brass is more user friendly.
When you are looking at these materials be sure to inquire exactly the material of the mod. For Copper you want C10100. This is oxygen free copper and is the purest one can find. Best conductivity of all copper as well. Some makers are using lesser quality copper that will turn green from tarnish. 101 copper goes black. After heavy use for a couple days of no cleaning, the tarnish will come off on your hands. My thumb crotch will get black after a few hours.
For brass you want 464 Naval Brass. Good conductivity and tarnish resistance. With a good mod, it can perform negligibly less than copper. With either material Cape Cod Cloths and microfiber will be a good purchase.
Lastly, with copper, be prepared to either up the resistance of your build, or lower the nic levels. I was at 18mg when I started and have now moved to 6mg. Not because I am looking to quit (luv the nic), but because the hits are stronger due to lower resistance of the mods.
The fact of the matter is that oxygen free copper and pure unalloyed copper both oxidize at around the same rates. Most common copper oxide is black, which will appear brown at first. The green color often seen on copper is cause by copper oxide reacting with carbon dioxide. Oxygen free will do absolutely nothing to stop copper oxides from forming. As far as conductivity goes, oxygen free copper is worthless for a mod. Copper oxides are very conductive.....
The oxygen free craze in audio cables has been proven time and again to be a marketing gimmick, a way to charge you 10X more for no benefit.
The main reason I wanted a copper mod is so it can have character. If you like the shiny copper finish then yes it will be high maintenance.