My favouite main pokemon region is Johto. :P Its my favourite because it was actually connected to another region. Not only that, it felt more like a continuation of Kanto and everyone loves Kanto :P Plus, it is homes to some of my favourite towns and cities, most notable Olivine City, Blackthorn City, Goldenrod City and Ecruteak City/town (I forgot :S) Plus, it has Espeon :D
My second favourite region is Sinnoh, mainly because it was so diverse (large cities, snowy cities, western-styled cities, muddy cities, solar cities/beach cities and it had GTS. :D)
I just didn't like Hoenn, even though it had Blaziken :\