I have a P3P and got me a Mavic. Very different animals, but mostly in regard to size. I love both, and use both professionally. It's hard to pick one over the other for "overall flying pleasure", what I mean you'll be well served by either IMO. Or better yet, both lol.
No doubt the Mavic is more advanced and a bit more stable, not that it matters much in the end but the portability does, as it means another "drone experience" altogether: it's more stealth in many ways (that's important trust me...), a lot faster to put in the air and land, considerably easier to carry around due to low weight and small size. And it's a blast. But it's a bit more sensitive, both are sturdy but the P3 is a Panzer. Not to mention the easy and accessible P3 knowledge base and replacement/spares/upgrades bin out there.
And the image (photo/film) quality isn't too different between the two. In photography a better tool doesn't mean better output, sometimes ppl are way too obsessed about the machine and the camera. There's a lot of awful and awesome videos from P3s, P4Ps Mavics and Inspires alike out there. Realistically, any of these drones and cameras are hardly the limiting factors.