Americans, definatley.
While I enjoy playing the Final Fantasy series, you have to admit the gameplay is a bit overrused and sort of stale,
in the U.S.
RPGs range from: Fable, World of Warcraft, (the upcoming Star Trek one), Fallout 3, Oblivion, and many many more.
All of these plots are completely different - the standard Japanese rpg plot is some young boy who is out to save the world, etc.
Also, look at some of the other games the States have produced.
The Halo trilogy, Gears of War, the GTA series,
It's sort of an easy view point for someone to see the quality.
However,
The Japanese are not short when it comes to creativity.
Less known games like Yume Nikki are incredible and produce (odd) yet interesting takes on gaming.
Though, I believe in the long run and in the current state of things - American Games are just so much better than Japanese ones - plot, graphics, and gameplay really make a difference and the States know how to make games that work.