I don't have all of them but I know at 5500AP there is 3 dragons breathing fire and I am going to get that one but I also like the dolphin and the turtle at 10,000AP.
Well I've never changed my Armatar except for Halloween(because it was Halloween!), so this obviously has to be my favourite if I'm willing to put up with it so much >_>
To get it: 0.00 x 0.000 + 00.0 - 0 /0 - 000 + 0 = amount of AP is needed