Both brilliant games. I didnt expect such a large poll difference.
To be clear: Smash Ultimate is probably the best Smash has ever been. It has an incredible roster, tremendous stage and music variety, it's nicely balanced (except for a couple bottom-tier characters that really need help), and finally produced a single-player adventure that seems well-suited to the type of game Smash is. It's one of the best games on Switch, and deserves its incredible sales.
But Breath of the Wild was a revelation. It was Nintendo doing something with Zelda I no longer thought it was capable of doing, breaking away from the Ocarina of Time formula and rethinking the series from the perspective of someone playing that 1986 NES gold cartridge for the first time and going on a grand adventure into a wide-open world with few clear paths.
We can quibble about some of the smaller decisions, and I have no doubt some will in the next round. But taken as a whole, Breath of the Wild is in a league of its own.