Copper is excellent from a conductivity perspective, but it’s soft enough that a long length of it can stretch from its own weight. One nice thing about copper is that even if it oxidizes at the connections it still has good conductivity.
Aluminum is another excellent material from a conductivity perspective, but aluminum oxide is an insulator, which must be dealt with.
For a wire antenna, copper clad steel is one of the very best. At UHF current flows on the surface, rather than throughput the material, so copper clad steel wire sacrifices nothing and resists stretching.
But constructing an antenna is about more than just the material. A lot depends on what kind of antenna you want to build and just as much depends on the frequency needed. If you want a really good vertical antenna for a single UHF band like GMRS, you can easily build one using copper pipe or aluminum tubing. The lengths are short so mechanical stresses are almost nil.