Man, nothing beats that pure sense of awe you get from a first contact done right. I'm drawn to the ones that feel truly alien, where the communication barrier isn't just a language puzzle but a fundamental clash of consciousness. Adrian Tchaikovsky's 'Children of Time' floored me with that—it's contact with uplifted spiders, and the entire framework for understanding 'intelligence' gets turned on its head. It's less about a handshake and more about recognizing a completely different path to civilization.
For a more classic, mysterious vibe, 'Rendezvous with Rama' by Arthur C. Clarke is still unmatched. The sheer scale and silence of the alien artifact, the utter lack of direct contact with builders, creates this profound, almost religious wonder. You're left with questions, not answers, and that lingering mystery is the whole point for me. It captures the loneliness and grandeur of space better than any shoot-'em-up alien invasion ever could.
Forget the aliens for a second. I think the most compelling first contact stories are actually about us. How do different human factions react? The scientists, the military, the politicians, the cults that spring up overnight. A great book uses the alien as a mirror to fracture human society, to show our best and worst instincts under ultimate pressure. The contact itself might be brief or even silent, but the human ripple effect is the real story being told.