The best month to travel to USA is during the summer months, as this is when most people are on holidays. However, keep in mind that this is also the busiest time of year and accommodation and flights will be more expensive.
If you're looking to save money, consider travelling during the off-season. Holidays to America are typically cheaper during the winter months, as this is when most people are not looking to travel.
With a little planning, you can find US holidays that suit your budget and give you the holiday of a lifetime.