I'm not sure if he's the "best" - at the end of the day, how you
define best is subjective - but there's no doubt in my mind Senna's
given me more value for my money in terms of entertainment than
anyone.
Personally, my favourite driver is Hakkinen(simply because I saw
more of him than Senna), but Senna's capacity to entertain and
produce moments of magic are simply unrivalled.
At the end of the day, I still think it's the mercurial and
unpredictable driving of people like Senna, rather than the dull,
monotonous yet consistent deployment of superior machinery - think
Prost and Schumacher - that sustains my interest in the
sport...