The only movie I haven't been able to see thus far was the 5th. i really should read into it a little more methinks.
I enjoyed 'The Wishing Star of Seven Nights' the most~ It had a great character driven story and for once in what has ben forever, Ash wasn't actually the main star of the film. Rather it was, quite surprisingly, the ever prop-like Masato. What was really refreshing about his role, was that the writers actually developed his character incredibly well. His interaction with Jirachi was very heartwarming, as was the relationship between him and Haruka. And of course, there was the history between Butler and Dianne, and coupled with their personallities, they made for great characters. All in all, it was just a really enjoyable character driven film~
Though, thats not to say I didn't like anything else about it. The visuals were very impressive for one thing, and the scenery throughout the film was nice to look at. It was fun watching some random, barren wasteland suddenly turn into this huge, lively amusement park for example. And the flight scenes involving Flygon and Salamence weaving inbetween Meta-Groudon's tentacles whilst firing off their attacks was just plain awesome.
Mew and The Hero of the Wave! Lucario! does come in a very close second however. The setting was creative, Luca himself proved to be an enjoyable character and watching the story unfold was both touching and exciting at its strongest momenets~ Luca didn't come of as some angsty loner pokémon, and you could greatly sympathise with his feelings about humans and his life on the whole.
Also, the Regi Trio rock my socks. "clickclickclickclick REJICEU RE-REGIIICEU" They seriously need their own fun-time variety comedy hour show.
Pokémon 3 gets an hounerable mention also~