Arneson and Gygax are like Steve Jobs and Bill Gates. The industry would have gotten here sooner or later, but these were the names that made it happen. I'm going with Mearls and Crawford for modern D&D, because the modern renaissance wouldn't have been possible without a good product to put into people's hands. Hickman, Weiss, Greenwood, and Mercer are certainly appreciated, but they are the sauce I put on my meat when I'm not making my own.
Greenwood is a pretty cool guy, and I don't want to discount the importance of a good melting pot setting. But melting pots mean people set up shop in your sandbox and play with your toys, making it impossible to tell where your contribution ends and theirs begins.