Well, technically, a .com website is supposed to target the worldwide and .US is for the USA. But there should be no variation between .COM and .US websites these days. It's just, Google puts more amount of trust to .Com, .Net and .Org domains in the past, but using .US domain is fine. In fact, there are some websites today using a .US domain sits on a higher rank on Google SERP. So .US is a good option.