so far, if we're talking successful catches, it would have to be my Timburr before the Nacrene Gym. Took all 15 of my pokeballs and the 2 great balls I found on my travels to that point.
Unsuccessfully, it would have to be Sigilyph (sp?) in the Desert Resort. When it was in the red, i threw an Ultra ball, it broke free without rolling even once, and the sandstorm killed him. >:(