For me, the best and most popular link shortener on the planet, because in addition to its basic services can be integrated with all social networks like twitter and facebook and shorten all the links we publish, showing us an analysis of how many and where they come from Clicks. It maintains a platform to measure the impact of our publications on different social networks.
It should reward its users a bit more, as well as other shorteners, since, because they are popular, they can give incentives to their most loyal users.
One of the disadvantages of this and all the shorteners is that they can be used for malicious purposes to infect with viruses towards pages that are not what the user thinks is intended.
Despite its popularity, many people do not trust links shortened for fear that it leads to malicious pages.