I will be interested in your input on this. I have both and like them both. They are just different. Each has it's specific areas that they are better than the other. Just remember what forum you are on and be careful how objective you are, you may get lambasted by a few here but most are pretty open to others input.
So here's some initial thoughts and impressions. I didn't have too much time to experiment since the weather in Florida has been total @#$% for the past 2 weeks, but here's a few quick things:
Look/Feel: I still like the look and feel of the Solo better. Construction feels a little sturdier and I prefer the black look over the white of the P3. But I guess that's mostly a personal thing. Some people I'm sure will like the bright white better. I was also a bit surprised that the P3 is a bit smaller in person then in images. One thing I really prefer on the Solo is the landing legs. I feel that it's a bit sturdier on the ground with the legs spread out a bit and on angles. The P3 gives me the feeling that it could tip over and any time lol, but it doesn't.
Setup: Pretty simple. The DJI app is really nice, and has tons of customizable features, very similar to the 3DR app in many ways. I'll have to dig in a little deeper to see if there's any pros/cons to one over the other.
Flying: The P3 was pretty easy to get in the air. Your basic FLY, LAND, and RTH functions all worked perfectly smoothly. We took off and landed from the grass on the fairway of a golf course, so I was actually really impressed that the P3 landed on the uneven surface without any hiccups. My Solo FOR SURE would have had trouble landing on the surface since it wasn't perfectly level. This could be because of the infrared sensors on the P3 that spot the ground. I did notice that the P3 sort of bounces when it lands, whereas the Solo comes in pretty smooth (when it works). Not sure if that's typical or not.
GPS: It actually aggravated me that the P3 picked up GPS so quickly. Within a minute we were flying with 17 satellites locked. I'd have to go back to the exact location with Solo for a comparison, but I've never seen anything more then 12 sats on Solo.
Gimbal/Camera: I definitely prefer the quality of a GoPro over the DJI camera, just based on a quick initial impression. Maybe there's some camera settings on the P3 we need to explore more, but it just didn't look at vibrant as the GoPro. The footage was also REALLY shaky, which is something I didn't expect. Most other footage I've seen from a P3 was fairly smooth, so maybe it was just some slight wind....but hey, on the bright side at least the gimbal actually worked, which is more then I can say for my Solo sometimes!!

Overall, I still prefer the Solo, but I do have to admit the P3 makes a compelling case for DJI. It's a really solid product for sure.