Go with soft. Copper and gold are among the best choices. They are excellent conductors and soft enough to really let the terminals grip.
Rhodium on the other hand is a terrible conductor and far too hard to keep a strong grip.
IMHO, besides simply solid copper spades, the WBT spades with spring loaded ends are the best.
Good bananas are however acknowledged by all knowledgeable and refined audiophiles to be the universally superior terminal. << tongue in cheeck>>