Actually I am sure that both men created lots of things. But what one thing stands above the others for each man? Or a better question, do you know more people that have used Linux or emacs? Those original tools were key parts needed for Linux to happen. But it was Linux that busted into the mainstream.
Stallman was building an operating system. Linus contributed a kernel for it. The Linux kernel and most open source software is built with gcc. I'll still agree that writing the kernel is no small feat. Otherwise the other two or three kernel options considered for GNU would have been completed before the linux kernel.