Most people begin with either anime or manga. Once you"ve watched a certain amount of anime, you will eventually discover a series interesting enough to compel you to read the manga. The obvious problem with anime would be the 7 day wait between episodes. Most anime seasons last 12 to 13 episodes. In some cases there will eventually be a second season, but that can take years. Thus you"ll swap to manga to find out how the story continues. It"s common sense that if you read one manga, you are obligated to read a second. Eventually the cycle will repeat itself and you"ll realize that some mangas are actually adaptations of light novels. If I had to rank them, light novels would always rank first. Second place would be a bit harder to choose, but I"d probably have to pick anime. Thus last place would go to manga.
Light novels generally have a much faster update rate and also a whole lot more content. Mangas are generally more of a summary of the story. You"d see more than 5 light novel chapters that each take 5-10 minutes to read compressed into a single manga chapter that takes less than 5 minutes to read.
I actually enjoy all of them, but I"d say it really just depends on the situation. It"s like how watching a movie after you"ve read the book can be really disappointing.