Hard to say...though I am actually pretty fond of Known Space.
Not quite sure why. I mean, Larry Niven did put a crapton of thought into the universe, even considering it's basically an alternate "our universe," and it's a timeline technically spanning over a thousand years if you measure from both chronological ends ("Safe at Any Speed" was around 3000 CE). Neutron Star is one of my favorite short story collections, "The Warriors" and "Madness Has its Place" are two of my favorite short stories, and World of Ptavvs is one of my favorite novels.
The Ringworld books also range from good to decent (the first two were better than the second two), though they're just one aspect.
Also, opportunity to prove your nerd credentials!
General Products hulls are vulnerable to only three things. What are they?