What browser should I use?

For Windows or Linux I highly recommend Librewolf.

Librewolf

Also for Windows or Linux, Ungoogled Chromium is a good option since some websites work better with it.

Ungoogled Chromium

Be sure to add uBlock Origin to the browsers for extra protection.

For Android use Mull (F-droid) or Bromite, but Mull lets you use uBlock Origin which is by far the best ad/tracker blocker.

For iOS you can use SnowHaze, but it really won't matter as much since Apple just doesn't make it easy for privacy.

If you need anonymity use the Tor Browser and only the official one. Never use third party Tor browsers like Brave's built in feature. Always make sure you're downloading the Tor Browser from their OFFICIAL WEBSITE, as there are many fake websites out there that trick users into downloading a malicious version.

Tor Browser (iOS doesn't have the official Tor Browser)