DOES STAINLESS STEAL AND GUNMETAL TARNISH?

I'm on my way to get my boyfriend an engraved Flask for our anniversary from things remembered. The have leather ones stainless steal ones and gunmetal ones. I personally think he would like the Gun Metal one. And I like the Stainlss steal one but will they tarnish over the years? Shoyld I just go with the Leather one? Even though I dnt like it?