Probably a Pixel or a Pixel 2, and install Copperhead OS which is an open source Android with all Google stuff removed and many extra hardening options. It's really security focused.

Use only F-Droid applications.

For extra level of paranoia, carry a portable hotspot, and connect your phone to the internet through your hotspot via wifi. This would avoid baseband attacks.

Obviously phones are very insecure, but depending on your threat model this is a very good option.