Both the Pixel 4 and Pixel 5 have multi-frequency GPS L1 and L5 bands for substantially increased navigation accuracy, as well as increased usefulness in citizen science GNSS projects. Dual frequency GNSS receivers enable additional types of ionospheric measurements not readily available with single frequency L1 GNSS receivers.
The Google Pixel 4 has been noted as having a key flaw–battery life too often less than 12 hours. Even disabling features such as Project Soli / Motion Sense and having the latest Android 11 did not greatly increase battery life beyond 18 hours. Short battery life was historically also quite an issue across numerous iPhone models, but is no longer such an issue.
The Pixel 5 uses a high-midrange CPU instead of top-end CPU in Pixel 4–the Pixel 5 CPU seems nearly as speedy as the Pixel 4 for my workflows.
The display panel itself is used for the top speaker–this restricts fidelity of the speaker, making it greatly emphasize midrange frequencies. This is fine for voice, but if you wish to listen to stereo orchestra music, you’d benefit from headphones.
The Pixel 5 does not have the “squeeze for Google Assistant” or Motion Sense–that’s an OK compromise in my view.
The baseline battery life in the Pixel 5 is about 24 hours, which can be pushed to 36+ hours with battery saver–much better than Pixel 4. All in all, even if a used Pixel 4 is substantially cheaper, go for a used (or new) Pixel 5 instead.
Reference: dual frequency GNSS phone model spreadsheet