Depending on the weight used, I did between 12-30 reps in total (the heavier the weight, the lower the reps), alternating legs, standing.
I did them using both DB and BB: DB Backward Lunges, and BB Forward Lunges (onto a box).
I personally found that Alternate Backward DB Lunges worked best for me re muscle separation and definition. However, you really need to just experiment and see what works best for YOU. And there may be an even better exercise to achieve what you want re muscle separation.