Why one leg is better than two
Cricket is a game played on one leg.
OK, that's not quite the whole story but as sport science students know: Running, throwing, batting and bowling movements occur with one leg applying more force than the other.
This means that training that involves one leg at a time is more specific to cricket.
Exercises like single leg squats, lunges and step ups work well. So would plyometrics based on single leg movements. You could easily replace the squats in my yearly training plan with any of these (although if you are new to training build up your strength with squats first).
Really it's not about one leg being better: I find having two legs is much better for balance. But when it comes to initiation of the important movements that make your game better, single leg training will give an edge.