Your username/avatar combination always make me laugh, I love it.Suicune on silver, latias, latios, mesprit, cresselia, registeel, regigigas. i caught all of them with my first ball.
...oh, without using a master ball? probably Rayquaza or palkia.
Hardest: Heatran. I had like 30 ultra balls and 10 timer balls and heatran was at really low HP. i had to reset like 10 times before i caught it..