Extension Methods vs. Traits & Implicit Conversions (a Scala question)

I personally prefer the idea of extension methods (most obviously in C#) vs. Scala's use of both traits/mixins and implicit conversions to achieve the same result. Simplifying the argument for each side, I find this:

• Extension methods: Simpler, less bloat, more predictable, extensible by third parties.
• Mixins: More flexible (since classes can override). Designer control for uniformity, but less extensible. Bloats compiled code. More complicated than static extension methods.
• Implicit conversions: Extensible but results in more complicated semantics. (I understand that C# also has implicit conversion, but it's not meant for this use case to my understanding.)

So, Scala folks, why should I prefer mixins/implicits (the Scala way), and how do you decide how much to mix in and how much to extend by implicits?

My own idea is something I call a "role" which is a combination of a runtime-erased type alias with optional extension methods. But I won't go in depth right now.