I believe that Copper has 2.5 times the conductivity of brass.
Copper, being an element is also more noble than brass, which
contains zinc, a metal that will erode(corrode?) in the presence of salt.
Tinned terminals are even more corrosion resistant. Couple that with tinned
Copper wire, and you have a very reliable connection, after you crimp, then cover
with dual wall heat shrink.
FTZ connectors, Blue Sea Systems, and Ancor Wire are good sources of information.
Especially Blue Sea Systems.