The best Adobe pen would be Ink&Slide. It has options built for Sketch.
No stylus works as well as the performance you get from a Wacom Tablet/Cintiq & computer, but it's an iPad.
Ink&Slide gives you bluetooth pressure sensitivity.
What's the status on the ink and slide intermittent issues with iPad Air 2? Has there been any resolution to this problem from Apple, Adobe or Adonit?