But if I should measure it from time spent with the racers it would have to be "Jaguar XJ220 - Amiga" as mentioned earlier here.
I didn't mention XJ220 in my earlier post. It was a great game but I only ever played it in 2 player split screen. We found it much more enjoyable and used to devote a Saturday to playing a whole racing season as team mates. Very competitive and often very close on points right to the end.
Also version of Wipeout on the PSP and Vita. Works brilliantly on the handhelds. I've played this for a lot of hours.