I don't think comparing stats is appropriate here. Both Senna and Clark were killed while they were still racing. Had the tragedies not occurred the stats would be different, though impossible to predict.for me it has to be Jim Clark with 25 wins from 72 Grands prix starts which is around 35%
Compared to Ayrton Senna 41 wins from 161 Grands prix starts which is around 25%
Interesting fact, he was the first former Formula 1 champion to die of natural causes... While racing at 187mph. Way to go."The Bear" Denny Hulme.