By most standards, gold is actually weaker than platinum. A good question to think about is what does 'stronger' mean? If you made a loop out of gold and hung a heavy weight on it, how much weight could it support before breaking? This is known as tensile strength and platinum has a higher tensile strength than gold. If instead you want to know hard hard you have to squeeze gold in one place to make it a little flatter, then a standard test is called the Vickers hardness test (which just measures the force required to make an indentation in the material). By this standard platinum is again stronger than gold (higher Vickers hardness).
In terms of more precious metals, Rhodium has recently become quite expensive because of it's usefulness in new technologies (catalysts, to be specific).Hope this helps!