In 1988 they were fairly close in the races overall (SennaFan24 might produce some analysis to disagree though!), but in 1989, Senna just had the bad luck.
They were closer in 1988. But reliability decided a lot of their duels.
Prost had more mechanical DNF's (2), and an apparent gearbox glitch at Japan. but Senna had more race-hindering issues overall (Oz, France, Brazil, Spain and Portugal). Overall, their luck was about even. The difference was that Senna played the game a bit better (best of 11), and finished ahead of Prost more often in straight fights. The only two races in 88 where Prost beat Senna on pure merit were Mexico and Monaco (the latter of course was because Senna binned it, but the onus fell on him for that).
In 1989, it was 7-2 to Senna in races where reliability did not decide the result (Despite Prost's gearbox fault during the latter stages at Germany, I still count it as a Senna win. Prost only got track position due to a botched pit-stop,)
Edit: To be clear though. Prost did out-think Senna from time to time. Monaco 1988 was a key example of such an occasion.
Edited by sennafan24, 08 December 2015 - 01:41.