No doubt in any of these. The two dragons probably aren't so easy to get hold of, so I'm happy to use Gigaiasu in place of one of them.
Jaroda caught my eye immediately as pretty cool-looking. Its offensive power may be non-existant, but it learns some pretty awesome support moves, and I've always had a soft spot for Grass types.
Rankurusu was one of my favourites early on, and it hasn't been overtaken by many. Great Special Attack and reasonable bulk is great, and Psychic types are always much more useful in-game than competitively.
Doryuuzu is a favourite of mine because of its mean-looking face, blade-like arms and huge attacking power.
Shibirudon is definitely among my top Pokemon in the whole game right now, and that's not just because of its zero weaknesses. I really love its design for some reason and its stats certainly aren't too shabby.
Sazando and
Ononokusu simply satisfy my love for Dragons.