Which ones do you think is the best, and what can be done to make hosting providers better in general?

Currently for me, it is a tie with YouTube and Niconico. YouTube has a better infrastructure, in part thanks to the data behemoth that Google backing them, has a better API and better support for video quality/formats, and at the moment provides a service which does not cost money and has blockable adverts. Niconico, however, trumps them in tagging, organization, frames per second, and playlist organization/presentation, while costing $5 a month for 24/7 decent service. It seems like YouTube intentionally tries to guide users towards advertised star series and personas, and tries to force Google+ upon users, destroying any semblance of a community that was once present on the site for a more efficient monetary scheme. Niconico seems to let the community do their thing, and only steps in when rules or copyright are violated; they have no financial incentive to do otherwise. Although Niconico has a very clunky UI, it is consistent and includes many nice amenities for the community, while Youtube consistently changes their UI for greater integration into Google, and many features come and go with the fashions. There are many other sites which have both good, consistent UI and are free, but they all lack the final deciding straw of these providers: content.

Youtube has almost everything that is not subject to abusive copyright, and has many of the popular videos of Niconico, though in a botched form. Niconico, however, has many high quality, highly integrated, cohesive videos that are rare to find outside the website. Looking at the comparison between MAD/YTPMVs, the only original Western equal to the massive MAD collabs such as Fourth Fairy Festival nicovideo.jp/watch/sm19711858 which I know is 8 Awesome Angles of YouTube http://www.youtube.com/watch?v=ysg0WZ_XmSU. Its a case of signal-to-noise, and while it is not quite right to say that either Youtube or Niconico inherently attract or repel quality videos, Niconico's intentional limiting of its demographic seems to work well in making certain content germinate to its fullest extent, while Youtube possesses the base of everything and the somewhat-best of many things, but not through any help of Youtube itself.

I personally greatly prefer Niconico's model, but I can understand why it would be hard to get it to work in the West, where online we expect to get have our cake and eat it too, and paying to watch unsyndicated online videos seems almost preposterous.