Correct Karate Stance for Sparring etc

hello,



I do Shotokan karate and am wanting to get better so I can start entering competitions etc so I am just wondering what everyone's thoughts are on this, when I am sparring the senior students always say to me I should have one hand guarding my mouth and the other sitting guarding my stomach however I have always used the basic boxer stance ( two fists at chin to protect face ).



I am wondering what would be the best stance for getting better at sparring and entering competitions etc for karate ?