Have an Answer?
I would begin by asking the following questions: "What age group do I best relate to?" "What age group allows me to be myself?" "Where am I the most comfortable teaching with regard to knowledge?" and "Where do I tend to display the most patience?"
If you're truly unsure of the grade level you might want to teach, arrange to visit and observe classrooms at various grade levels at schools in your area. That should help you gain a perspective about what it's like to teach different grade levels.