When creating an artist portfolio to demonstrate your individual art style, the most important factor to guide your selection is "the art style you like to draw in most that makes your work unique." This approach showcases your personal voice and artistic vision, which is crucial for differentiating yourself in the art world.
While understanding other art styles and techniques can be beneficial for inspiration and growth, your portfolio should primarily reflect your unique artistic expression. Copying famous masters can be a valuable learning tool, but it may detract from showcasing your individuality. Including a very large variety of art styles can dilute your portfolio and make it harder for viewers to understand your specific style.
Ultimately, your portfolio should tell your story as an artist, highlighting the aspects of your work that resonate with you the most and that you believe define your artistic identity.