I don't believe what your uncle says to be true, and I would go so far as to say that there is no reason to believe such a thing. There may be cultural value in this idea and I would still look at the claim and see if there's anything you can learn about the culture you're growing up in and the values of your family and society.
Hard work is considered a value because given very simple economic conditions hard work is a good predictor for creating wealth and being able to live a comfortable and content lifestyle. That is why you will find similar ideas around the world.
I believe you should challenge the expectations of society, but not just for the sake of being contrarian. Look critically at what you're being told, but always consider that such expectations and beliefs often survive because they are useful, and in that sense often to some extent true. But ultimately you should prioritize doing the thing that pragmatically brings you the most contentment and fulfillment - quite often this may not be what society expects or wants from you, because society wants to use you as human capital more often than it's interested in your own wellbeing.
As far as what animal you would want to be in your next life, Arthur Schopenhauer makes some interesting points about the differences between the human experience, and those of most animals. Something to the effect that
"Animals hear about death for the first time when they die."
While to some extent I don't think this is actually true - more the point is that animals have the benefit of not experiencing the same self awareness that humans are subject to. Many humans have to spend their days contemplating or denying their own mortality, and having to grapple with complex ideas of self-identity, morality, religion etc. Animals as far as we can tell are not burdened with any of this. So in some ways it might be preferable to have the life experience of some animals rather than the human experience.
Even with that being said - perhaps it's the egoism of being a human, but I rather think that I agree with your first instinct that I would prefer to be a human. This is peculiar given how many burdens come with being a human, but I believe as humans those burdens are also such a pleasure, full of potential and rich with interesting puzzles and fascinating contradictions. To be a human is sometimes like being gripped by the pages of a well written novel - even when the story is mundane or tragic there's something gratifying about seeing time and the world unravel before us.
