Valuing abstract measures of the welfare of a group distinctly and separately from the welfare of the individuals making up that group is a particularly pernicious conceptual invention. Its most recognizable modern incarnations are nationalism and patriotism, but it has been serving as cover for inhumanity and disregard for considerably longer than that. It also serves as a way for people to argue against treating aging as a medical condition: the group is just fine, thank you, and thus it doesn't matter that all of the individuals in that group are doomed to suffer, diminish, and die. So why do anything about it? A healthier view of the world is that only individuals and their interactions with one another matter, but making that the default mode of thought is something of a challenge in an era of strong centralized governance and wall to wall propaganda for the nation state concept as an entity more important than its citizens.
One of the innumerable romanticizations of death that we're often presented with is that, as one generation dies out, it's just passing on the responsibilities of life to the next. Someone else will take on the task of perpetuating the species, and in general, it doesn't really matter who it is. Never mind that we all die; as long as there's someone to pass the torch to, somebody who will continue to play for team humanity, that's all it matters.
Humanity is not a football club, and neither are other, smaller groups of humans. The family of my great-grandfather, intended as himself, his wife, and their children, is dead. Their genes are still around, and other families have descended from them, in some case even bearing the same family name (another abstraction), but the specific individuals making up my great-grandfather's family are gone, and so is that specific family. You might argue that they're still alive in their descendants' memories and genes or that their name is being passed down, keeping alive the family, but these are all mental gymnastics to present the fact that they're dead in a less unappealing fashion. They're dead, and whether someone still remembers anything about them, or carries a few of their genes or their name, doesn't make them any less dead.
On the subject of future generations, one often hears that their well-being depends on our actions today, and thus we should work to leave them with a better world than we had; this is a commendable intention, and, in fact, it is one of the reasons why we should develop rejuvenation - to spare future human beings the plague of age-related diseases. However, future generations are not here yet; we are, and it's rather mystifying how everyone frets about the currently nonexistent needs of people yet to come but not so much about the very real needs of people who already exist. Today, people suffer from, and die of, age-related diseases; it's a concrete problem, with tangible effects on the world at large in the present; yet many people seem to worry more about the potential problems they imagine that rejuvenation might cause to future.
So, who's more important? Individuals or humanity? It should be clear by now that we'd better think in terms of individuals. The good of humanity shouldn't be about maintaining our presence in the universe just for the sake of being here; it should be about the well-being and life quality of the individuals that make up humanity - and when they're dead, or about to die, individuals aren't generally doing very well. Being concerned about future generations is both understandable and commendable, but it should not lead us to neglect who's already here. As long as we exist, and our good is taken care of, the preservation and the good of humanity will be ensured as well; future humans are welcome to join.