I've heard it said that either of these techniques are able to get one up the mountain or across the river to liberation. Without any real depth of experience with them myself I conceptualize shamatha as a process where one slows down mental phenomenon to a point where it becomes much easier to see through them. Vipassana I see as a process where one becomes better at seeing through things where effectively mental phenomenon slow down. I imagine it something like at the end of the Matrix where Neo finally sees the code and things slow down for him .
Anyway, I tend to have a busy and curious mind and shamatha has been pretty elusive as a practice, I mostly focus on vipassana. So I'm curious as to others understanding of these methods and personal experiences with them.