Check out this great review of cintiq companion, Microsoft and IPP. I have all these devices also and couldn't agree more with his review. For the reviewer, he prefers the IPP for his work flow, but points out its many flaws. And the flaws of each competitions tablet.
After finally getting my pencil I've decided I'm keeping my IPP for light mobile sketching, as this is where it excels, but the cintiq is a far better fit for my daily painting needs and still gets 90% of my time. This is an individual thing, since everyone has differing needs and workflows, so don't hate on me.
for me, The pen is far better on Wacom, it does tilt and rotation. It has More tooth on the screen, better pressure sensitivity, programable buttons, eraser, rotation, is ergonomically better, all this is found on more much powerful hardware, and uses software without limits. No other tablet can do that. any one saying the iPad pencil is flawless is either being dishonest or has not tried the other options. IPP does have less parallax. This is nice, but not a huge deal to me. Just look at the cursor.
Don't get me wrong, I love my IPP, but it does not live up to this hype for artists. If this thing had rotation pen feature, a screen with more resistance, buttons, eraser, double the ram and cpu speed, and ran professional software, I would ditch Wacom in a second. Procreate is too limited for my work.
I give the apple pencil 7.5/10 a "C" average. 7/10 for SP4, WACOM 8.75/10. If Wacom had no parallax it would be 9.5/10 for my needs.