Depends on where you want to practice. If you want to practice in America within the American system, then obviously being educated by the American system better prepares you. Just like a French medical education would help you better adapt and practice within the French medical system. Its not just the art of doctoring, its the bureaucracy, documentation, procedures and regulations that make a difference.
If you're looking at pure "knowledge", then in my humble opinion US medical grads have access to a great deal of research and technology that they can effectively leverage. While the intelligence level of docs across countries may be similar, I think that access to resources is also a contributing factor to "knowledge". However, thats just my $.02
Last but not the least, I hope I didn't just feed a troll