As the title says! My choice, for now, is Leta, directly from Mullvad. I really like because there are no ads by deafult, which is particular important since those ads usually lead to malware.
Otherwise, i like mojeek (same reason).
They both have a strong privacy policy and search results are good enough for me.
Leta: https://leta.mullvad.net/faq
Mojeek: https://www.mojeek.com/about/privacy :)
I use SearXNG and Startpage.
Startpage is really nice. I use it when sites blocks VPN users like me since i can proxy every page i visit through them!