Renting a car is the best to get around in Los Angeles. LA's public transportation is not as developed as many major cities from around the world. Given that LA covers such a large geographic area, a car allows you to experience a lot more instead of spending wasted hours on bus/train connections.
For example, you can get to Hollywood rather easily via subway from Downtown. But there is not a direct public transit route from the Hollywood area to the Santa Monica Pier. This example shows the difficulty a visitor might have it they want to go Hollywood and the beach on the same day. It especially makes it difficult to see a lot of sites if you only have a couple of days in Los Angeles. Reputable car rental company links below: