Q: for me it was 1999, two drivers and teams fighting for championships to the last round (Hakkinen+ Irvine), 6 race winners, and a comptetitive ford/ cosworh powred car in the Stewart SF3 (when instead of what might of been better)!
A: 1983, when 3 drivers went to the last race of the season with a chance of the title. Arnoux had to win at Kyalami, with Prost 6th or lower and Piquet 3rd or lower...Piquet had to score three points more than Prost...Prost just had to finish ahead of them both. In the event, Arnoux and Prost both had mechanical trouble and Piquet gave up his lead to preserve his car (much as Villeneuve would later do at Jerez in 1997), finishing third to claim the title by 2 points. Piquet had chased down Prost's 14 point lead with 3 races of the season to go (and on the old 9-6-4-3-2-1 scoring system), winning two and finishing third in the other while Prost only managed one second place. Eight drivers won GPs for 6 different teams, and it was the year turbos finally came of age, with Piquet the first turbo-powered drivers' champion. In Detroit Alboreto took the last normally-aspirated victory until 1989, when turbos were banned - Watson and Rosberg also won in non-turbos at Long Beach and Monaco respectively.