I have both the 1st gen AirPods and the AirPods Pro. For background, my ears are "compatible" with the AirPods, meaning they don't fall off and I don't need to adjust them while wearing them.
The AirPods Pro S tip is just a bit too small for my left ear, and the M tip is just a bit too large. I use the S tip and there are days when I manage to seat the pod securely and all is well, but more often than not while out on a walk or if I'm talking (so my jaw moves) I need to adjust it every 15-30 minutes. The S tip is perfect for my right ear.
When the AirPods Pro are seated properly, noise cancellation is great for in-ears. They completely cut out the hum associated with modern homes - ventilation, AC, appliances. Out and about they abate the background hum of traffic and make slowly passing combustion vehicles seem like electric. It really is eye-opening just how much background hum there is, especially outside, when you take the AirPods Pro off. With the AirPods you hear everything and I at least need to increase the volume of whatever I'm listening to to cut through the noise. With the AirPods Pro I can listen at considerably lower volumes.
When you want to hear your surroundings without taking the pods out of your ears, the Transparency mode is just wonderful. It appears to amplify sounds a bit and adds a slightly processed quality to them, but I'm really glad it's there.
In summary - AirPods don't fit everyone's ears, but even when they do that's no guarantee that the AirPods Pro will also fit perfectly. In my experience when they do fit, the AirPods Pro are a clear step up in listening comfort.