I used AirNav Pro for a while before skydemon came along on the iPad 1 and it was really slow to redraw the map - I upgraded to the iPad 2 and the performance became much much better. I think poor ANP performance is more hardware based to be honest.
I now exclusively use skydemon and completely agree with a previous post about ANP not doing any vertical navigation - to me that is ANP biggest problem. I also would love Skydemon to have a screen lock facility whilst in the nav mode to prevent inadvertent plan changes! Perhaps this is more an iOS issue than the app per se.