There is no difference in terms of specs (pressure, lag, tilt, etc.) between Pencil 1 and 2. Even the nib - people think it's different, but it's actually exactly the same.
With that said, Pencil 2 has a more pleasant matte finish, charges better and has a nice side gesture.
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The nib is quieter and has more resistance when pairing a Pencil 2 with an iPad Pro.
My Pencil 1 with 6th gen iPad feels like using a rock on glass.
This is not due to the Pencil itself, but rather the screen. The 6th gen iPad doesn't have a laminated screen wich makes the feel of the Pencil different (the sound it makes when it hits the screen is different, and perhaps the coating is slightly different, but I doubt it).