moyu fs, but i've seen very good cheap cubes being released by yuxin and qiyi (little magic wayyy back in the 2010s, qiyi with their warrior series), but moyu has cemented itself as quality with a reasonable price tag in most cases.
I have about a dozen cubes. The best of the best is my Dayan Guhong Pro+ 56mm. A very close second is my Ferrocore 2. It looses because it's 55mm. If it were 56mm or larger, it would win no question. Third is my Gan 16m maglev. But the Guhong is like $20 and the other two are triple the price. So for cheap, there is no contest. I did add edge magnets though. Check YouTube.