There's only one YouTube. But there are a lot of other web sites like YouTube. But why bother to look at sites like YouTube, why not just use the original? Well, if you're a professional video producer you may want to put your work out on a wide range of sites, to ensure the broadest audience. And if you are making home movies, you may want to put your work on a more minor site, to ensure that your video doesn't get seen by the world.
Which web site you choose to use depends on what you are looking for. This comprehensive list of sites like YouTube will give you an overview of all of your options. Some of these video sharing sites are designed to be exactly like YouTube. Others have developed their own niche and are not trying to compete directly with YouTube.
In choosing whether to use YouTube or another site, there are many factors to consider. For one, you want the content and tone of the site to fit with your videos. You should also consider the technical capacity of any video web site you use.