My fave region is (always) Jhoto, why?
Errm. dunno 16 gym badges, 251 pokemon, eggs, day+night, put pokemon on the map, funny name and the way u can catch both of the pokemon pictured. :)
*takes deep breath*
Second is Sinnoh, third, Hoenn and last Kanto. (sorry, but its just too I dunno, I...