I'm too scared to try legend so I settled for master twice.. only got 1 dragon out of the deal, doh.
First time I did master I used a safe mono black team. Then tried again using a haku/isis team, which was incapable of surviving a single attack from green or blue, but they didn't get to move (although the game was REALLY trying tos crew me on blue, you wouldn't BELIEVE how many green orbs it kept giving me. argh).
I think I'll just spam master though, great exp for me.