I would have to say that Pokemon's original series was of course a favorite, but I also loved Johto, Johto Champions, Orange Islands and Advanced. The series' that came after advanced were by far some of the ones I disliked. However, I am incredibly impressed with how strong Pokemon X & Y the series has started off. The battles are looking really fun, and the characters have some potential. I love the fact that ash is wandering around with the Luminose gym leader for a companion and the little sister is pretty funny. I'm looking forward to Ash's second battle with the Luminose gym leader and how it turns out when Ash discovers that his companion is the leader.
I particularly like Serena too. I totally ship her and Ash. If there's anybody I think would be a good match for Ash, i think Serena is it. She's just displaying what feels like a crush all the time and I think that her character has potential to work with Ash's since they have history of being childhood friends. I never seen Misty as a potential girlfriend, nor dawn, and not really even May although I love May a lot. Iris is DEFINITELY not a pick for me. I wasn't fond of Iris's personality. I also like the fact that Ash appears much more mature and older. There are still childish feels and moments in the series but that's part of what made Pokemon so great. I just see some major potential from X & Y and I feel it'll be worth the watch till the end. I'm always anticipating episodes.
That's just my opinion on this subject. ^^