Straight shower curtain rods are the traditional style that run parallel to the bathtub, while curved rods bow outward, offering more elbow room in the shower. Curved rods are ideal for smaller bathrooms where extra space is desired, and they can also help keep the shower curtain from clinging to the person showering. However, straight rods are often easier to install and can be more suitable for shower-tub combos or larger bathrooms where space isn't an issue.