The Porsche 911 is an icon. There is no debate, it is the Mona Lisa of cars. Far from perfect, it has stood the test of time, much in the same way as Francis Ford Coppola's Godfather movies. But there is always some debate about it being the best sports car ever.
I would even argue it's not the best Porsche.
Thirty years before Porsche committed blasphemy by introducing the Cayenne, a V8 powered SUV, they introduced the world to the 928, a front engined, water cooled, V8 powered GT. Then they had the audacity to call it the replacement for the 911. The motor press and Porsche purists called it an abomination, saying it was Germany's answer to the Corvette.
If you look at cars developed in the 1970s you will realize the conventional wisdom of the time was to move away from pure sports cars towards GTs. Jaguar had already done this, replacing the E-Type with the XJ-S. The Chevrolet Corvette became longer and more cushy during this era and the Datsun Z even grew back seats. The venerable 911 was thirteen years old when the 928 was introduced and it seemed obvious that it was nearing the end of the road.
If you look at the 928 through this prism, you will see it makes perfect sense. Porsche didn't just create a vehicle to fill a need, they engineered a masterpiece. The 928 is a technical marvel, far ahead of its time. Name me another car from that era with supercar performance, all day comfort and practicality, and room for four average size people in a pinch.
To use the Coppola analogy, the 928 is the Apocalypse Now of cars. Comparing it to the 911 would be like comparing Apocalypse to the Godfather. It's just not possible. But if you compare the 928 against its contemporary rivals, you will see it was simply the best GT of its time.