Returning Values - Which Is Faster? ByRef Sub Or Value-returning Function

What is a faster/better coding practice?

Method 1:

Code:
Sub myFunction(byRef x)
x = x + 1 ' do something with x
End Sub

x = 7
myFunction(x)
response.write x ' shows 8
Method 2:

Code:
Function myFunction(x)
myFunction = x + 1 ' do something with x
End Function

x = 7
response.write myFunction(x) ' shows 8

Also discuss considerations when there are more than one variables that need to be changed.