In order to achieve peace, only the Templar's methods are the ones that could lead to "peace", but I don't think we can qualify that as true peace, because what the Templar's envision to the world does not correspond to peace, it's much more about control and order.
The Assassin's main goal is to preserve free will, even if that means a flawed humanity. Like the Assassin's, I recognize that by preserving free will, it's impossible to achieve peace.
In the end, both want peace, the difference is they use different methods, although the funny thing is, in my opinion, no one, neither the Assassin's nor the Templars can in the end achieve true peace.
Peace doesn't exist.
With this said, I might add that I sympathize with the Templars, like I do with the Assassin's, for different reasons, but in the end, I prefer to live in a world where free will exists.