Don't know if these are my favorites, but I do like the strange messages on the signs of Southern Island.
"Those whose memories fade seek to carve them in their hearts."
"All dreams are but another reality. Never forget..."
I wonder if these messages mean anything to Latios and Latias. There doesn't seem to be much lore about those two Pokemon in the games other than the Soul Dew. (Not sure if the 5th movie counts.)
"Death is certain; it's hour, uncertain."
The images used for Pokemon + Nobunaga's Ambition are BADASS!