both great effects, both i own, but i prefer distortion since there a lot of impromptu deck vanish effects that would have similar reactions with panic but the only thing with panic is you spread b4 the vanish(as aaron says its very visual)...unlike any other deck vanish effects but youd have to carry the gimmicks and i dont like carrying as much gimmicks on me but thats just me...its up to you to decide and also some say panic gimmick lasts longer than distortion but its all on how well you use the gimmick and care of them
all i can say is I own Distortion and love it and get great reactions from it... A simple transpo alone usually gets a great reaction, and when you follow it up with distortion, people tend to go nuts.
Since I don't have Panic, I can't say how easy it is to get in and out of, but it looks like it would be a bit more difficult than Distortion.
Distortion is great as the audience can actually see the 4 of diamonds transform into the 6 of diamonds. I can't tell you why Panic doesn't work well for me because it would be exposure.