It sounds like you like worldbuilding and epic (in the formal sense) themes. I'd start with the heavy-hitting classics and work your way into the more esoteric stuff. The most famous SF novels are, by and large, most famous deservedly. These include classic series such as Dune. Basically the top hits from Google.

My personal favourite would be The Culture novels, by Ian M. Banks - The stories have a wonderful mix of wit and hard SF, played out on the grand scale of the human-AI driven galactic empire known as 'the culture'. The novels deal to a greater and lesser extent with the galaxy-spanning ideological war between the AI-controlled 'Culture' and everyone else. The nominally freedom loving anything-goes attitude of the Culture, is actually in opposition to the way it aggressively expands militarily - imposing its specific brand of egalitarian freedom on the universe. It claims to remain neutral, yet actively runs agents to secretly meddle in the politics of different worlds. Since the first book (Consider Phlebas) was published in 1987, these themes have only become more relevant.

The Culture novels have all the major SF themes - smart computers, faster than light travel, post-humanism, post-scarcity - yet never fall into the trap of being hackneyed or cliche. The novels deal deftly with politics and ethics, but never degenerate into dull scenes of people arguing around tables about mining rights on the planet Arrrgh. They balance action and diplomacy, technology and society, without becoming either loud and dumb, or smart and dull.

There are a lot to choose from, I'd suggest starting with The Player of Games, which is shorter and more accessible than the rest - yet still a great introduction to the series and its themes. Alternatively go with the first book, Consider Phlebas and jump into Ian Banks' first SF novel, which puts you right in the middle of the genocidal conflict between the Culture and the Idiran empire.