I don't know if you can say either way is better. In the past I would have said the split jerk is better, but recent olympic champions (Dimas for one and then the 69kilo guy from China) seem to discount that theory.
The best way I can explain it is next time you're in the gym try and do an overhead squat ass to the grass with the your hands not much farther than shoulder width. Then do an overhead lunge. It's much easier to control the weight. You don't feel like you're going to lose it behind or in front as fuck because your weight is spread out over a much greater distance. I also feel that with a leg to each side you have more side to side balance.
Sorry I realize that doesn't really give you any hard reasons for why its better but hopefully it helps. Maybe Krollmonster or Galvatron can explain it better.