I'm not sure what type of argument you mean, but what I would say is that you should develop such a good argument that that's what carries your ... (I don't know, motivation and drive to say what you want to say). I understand the fear that if you stutter they may percieve you in a manner you don't like, but I would say just developm an argument that's so good that your stuttering doesnt really matter. A good tip is this: If asking your boss for a raise you can't bring just one thing to them for why you should get a raise, you need to bring atleast 3 things. It's the same as formulating an argument that leaves your opponent quite unequipped. Do some research and come up with 3 good arguments so that when it does arise you are equipped.