During the year as you train for debating you should experiment with all speaker roles. Part of debate is stepping out of your comfort zone, so embrace the challenges. You might be surprised about the results! You will naturally understand which speech you prefer and it’s a great idea to keep that role during a tournament. However during training, rotate between all speakers, you’ll never know when you’ll be called to ironman!
Do not be afraid to ask your coach for advice, they have seen your skills and direct you. At tournaments you might want to be consistent in the role you cover and not improvise, especially during impromptu prep where every minute counts. If you know which speech you will cover it will be easier to focus on the argument you’ve been assigned and the role you’re called to fulfill.