Above is a comparison table showing American rockets that are in operation, in development, and proposed. Most of this information is taken from FAA documents. I have added information for Taurus II, which is set to debut in September, and the proposed Falcon 9 Heavy based on company documentation.
Orbital Sciences Corporation’s Taurus II is a medium-launcher that is set to fill the market void is being left by the pending retirement of ULA’s Delta II rocket. The company has contracts to launch 8 resupply missions to the International Space Station. The figures for it are the maximum payload from Wallops Flight Facility using the most capable variant of the booster.
SpaceX’s proposed Falcon 9 Heavy would be the most powerful American booster if it is built, being able to lift almost 10 metric tons more than Delta IV Heavy. SpaceX is advertising the rocket at $95 million, which would be significantly lower than the largest version of the Delta IV.