How to correctly concatenate a String in Kotlin?

In Kotlin, you can concatenate 1. using string interpolation / templates

val a = "Hello"
val b = "World"
val c = "$a $b"

2. using the + / plus() operator

   val a = "Hello"
   val b = "World" 
   val c = a + b   // same as calling operator function a.plus(b)
   val c = a.plus(b)
   
   print(c)

3. using the StringBuilder

   val a = "Hello"
   val b = "World"
   
   val sb = StringBuilder()
   sb.append(a).append(b)
   val c = sb.toString()
   
   print(c)