You and your instructor will be spending a lot of time together in a small classroom, so chose a CFI that matches your personality. Different people learn differently, and different instructors teach differently, and when student and CFI differences clash, your training will probably not go well. If you can't understand a prospective CFI's answers to your questions, and the CFI can't reword answers so you do understand, you will likely have similar problems in training. If the two of you can communicate clearly, take an introductory flight lesson to see how you get along in the airplane. In the end, only time will validate your CFI selection. But if your CFI isn't working out, don't be afraid to change.