Lucifer's Hammer, for a discussion of how humans will react to a world-wide catastrophe.
Footfall for a possible scenario of invasion by an unexpected species, and humanity's reaction to it.
Reality and imagination operate in two distinctly different universes. The periodic statment that there must be a few planets suitable for life, meaning, provincially, life like us, is meaningless. We can't even imagine what other forms of life might exist, so like the drunk who lost his car keys, we keep looking under the street light, because the light is better there.
As a final thought, speculation is entertaining, but there are lots of serious and real problems that we need to deal with. Sooner rather than later.
Extra-terrestrial life is waaay down on the list of things I worry about.
I have read both.