My favourite generation is the one I have nostalgia for and the first one i played, Gen 3
Ruby and Sapphire i think had really good pokemon designs especially my favourite legendary Groudon, he looked metal as fuck on my copy of Ruby. I enjoyed the soundtrack from the GBA version and matched the anime based from it, Pokemon Advance.
What is your favourite generation and why? What details makes it stand out for you?
Generation three like you, except from the point of view of Pokémon Colosseum and its sequel. Those games were ahead of their time.