Olympic weightlifting, no question.
Oly lifting uses all the major muscle gropus of the body. Oly lifting trains the rate of force you can generate by working your fast twitch fibres. The amount of fast twitch fibres in the body driectly contributes to how well a person can do a vertical jump. Oly Lifting cultivates said fibers.
Read this article: http://www.bodybuilding.com/fun/henkin14.htm
I couldn't find Chad Ikei's original. But would recommend it too anyone if they can locate it. Would draw your attention to the following as well in the article:
Shane Hamman, 2000 Olympic Team Member and current National Super heavyweight Champion, another big man weighing in @ 163 kg (358 lbs) but only at a height of 5'9" tall, can jump onto boxes @ a height over 42" high. Of course Shane was also known for his squatting ability of over 1000 lbs. (Snatch 195 kg, Clean and Jerk 230 kg)."
He was also a 2004 Oly team member. So if you want to help your jumps, I would say to go Olympic!