After watching about 48785920390809797853474927852038324928 Indigo League repeats when I was 10, the 1st opening is just the teeeniest bit boring.
My favourites are: Johto Journeys, Johto League Champions, Advanced Challenge, Advanced Battle and Battle Frontier (should've been longer though)
Favourite Japanese openings: OK!, Ready Go, Battle Frontier, Spurt and Together - but only when I'm in the mood. Together sounds too happy sometimes...