Best: I have alot. Rayquaza, Lugia, Mewtwo, all the starters' final evolutions, all the regis, Latios and Latias, all the legendary birds, Raichu, Steelix, the Eevee evolutions except for Glacion (doesn't sound very close to the other's cries which bugs me), and Kyogre.
Worst: Unfortunately, alot of the 4th gen. They all sound like random squiggles here and there which sounds, how should I put this, wtf. But the worst for me has been Lopunny.