For me, it you're ranking purely by quality of layout, art and design (again the actually quality of the rules/material/content is extremely subjective), my rankings are;
1. Wizard's of the Coast
2. Paizo
3. Kobold Press
And then there's a big drop-off. The problem is if you're making material for 5E D&D, you're automatically working off of a different company's rule-set so are far less likely to attract staff and investment. Paizo is on this list, but they really run their own rival system to D&D (Pathfinder). And other companies with their own games, like Games Workshop, Call of Cthulhu, Vampire the Masquerade, and Savage Worlds can also pretty be pretty professional, but they run their own game systems (in the case of Games Workshop, they actually make way more money off miniatures than books).
So Kickstarter projects are the source for most more professional projects, as they can attract way more investment than other sources, and tend to be labours of love (at least the funded ones). Kobold Press is actually so professional today because they now tend to make their bigger projects on Kickstarter to give them that extra level of design quality that most smaller companies will not have.