I like Subs better, I feel that the Japanese version has better voice acting and emotions to the characters. Also because I can speak little Japanese and can write and memorize the full katakana and hiragana alphabet system, although I do not really understand a lot of Kanji.
I also enjoy the dubs, especially from the Kanto, Jotho, Sinnoh and Best Wishes series, even though they were not as good as the subs.
I absolutely dislike the dubbed Advanced series due to 4Kid's horrible voice acting, and also because the trainer's choice was a big epic fail. Arbok evolves into Seviper???