I won't call Prost a better driver, or a even close in skills or have better character.

Prost pioneered the crash your rival move when he intentionally try to crash Senna out of the Suzuka race in 89, he was lucky that the FIA president at the time was a French and protected him. A year later Senna returned the favor and let Prost taste his own medicine.

He is also the first diva in F1 teams, demanding himself to be the prefer #1 driver, his diva-ish behavior also got him fired from the Ferrari team in 91, not to mention he stole Mansell's race car in 1990 and forced Mansell out of WIlliams in 93. He also he block Senna from joining him in Williams in 93.

Some kind of character off the track.

Prost only won 4 world champions because of superior cars, he is nothing if he doesn't have a top car. Senna on the other hand made wonders out of junk cars, he was right on Prost's tail in 93 despite the McLaren being miles behind WIlliams. Even Alonso could squeeze a sub-par Renault to some half decent results.

Despite all that had happened between Prost and Senna, Senna actual forgave Prost and made up with him, now who is the better character, Prost who keep offending people or Senna the one who forgives?

There is really no contest, Senna is the best driver ever, Schummy come close.