Darkrai's Dream

Been playing White 2 for a while now, and I went to go catch all the Legendaries I could. I have 2 Master Balls, what do I use them on? Nothing. I pretty much refused to catch anything with the Master Balls until the point at which I failed to catch Kyurem with a Quick Ball. I remember I caught Reshiram with a Quick Ball (on the first turn of course), Latias with a Heal Ball, Virizion with a Nest Ball, and Heatran with a Dusk Ball. I don't quite remember what I used to catch the others, but I pretty much catch these guys with what I feel suits them. Or a Quick Ball if possible. So, anyway, I still have one Master Ball, and I haven't caught Registeel or Regigigas yet. But I will, just probably not with a Master Ball.