You can't go wrong with either haha
But if you're mostly in 'business-like' environments, I'd go for the metal band. The leather one looks good and has a better fit on your wrist, but this is leather, which means it needs maintenance if you want to avoid odors getting stuck in there and avoid getting it wet as much as you can (plus, scratches might show up more easily if you get a dark one). The metal one is a bit heavier and might not feel as much of a perfect fit for everyone, but it does look classier, it's sturdier, and keeping it clean and odorless is a lot easier than leather. Also, not as easy to scratch, and if it does, it's usually not as visible.