Wedding band? Which?

Pinky
I am trying to buy my fiancés and my wedding band... But ... What's best? 
​Titanium? 
​Tungsten? 
​Sterling Silver? 
​Stainless Steal? 
​rhodium plated? 
​ 
​we would like black wedding bands ...
​Please let me know your opinion! 
​Thank you babes!