IMO, Kagi and Brave search are the two best alternative general search engines right now.
Runnaroo was pretty good as well ;-)
Kagi uses a mix of Teclis and other engines (claims to use Bing and Google) but the ability to adjust ranking yourself is its wild card. Neeva is similar, combining its own index with some ability to influence ranking.
But personally, I'm trying to reduce my use of "one engine to rule them all" and instead use specific engines for specific tasks they're good at.
When I say "Best"for a general search engine, my definition is that it would fulfill the needs of myself and my non-technical family members. Kagi and Brave Search both do that while being different enough to not be just another Bing clone. I use Mojeek often, think it is great, and having their own index is a tremendous asset, but it doesn't quite meet that full definition yet.