Probably a toss-up. You are not looking for type-in traffic and both .net and .US are second-level extensions so it's just a preference of how you want to brand your site.
If you go with .net you are probably more likely to have visitors going to the .com by mistake. That's something consider.
If you go with .US there might be some people unfamiliar with the extension.
My suggestion is to consider the category for your site and then make a decision. If it's finance, government, health care, eduaction, etc. I would go with .US.
If it's consumer goods, travel, adult, etc. I would go with .net.
Good luck!