Which way is better for trace()?

1

What I mean is :

var a:int = 10;
var b:int = 20;
var c:int;

//------- METHOD 1 -------//
c = a + b;
trace("Sum", c);

//-------METHOD 2 -------//
c = a + b;
trace("Sum" + c);           // Here instead of comma I've used +

Using comma or plus sign; which is the most recommended way of using.
Why does using both is allowed?
If using ‘,’

I’d straight away do trace(“Sum”, a+b);
How to do like that using + ?

Please give your ideas on it.
Thank You