I don't really think the question makes sense. Most important in what context?
If you mean best known to the general public, then currently Hamilton/Vettel. Tens years ago maybe Senna/Schumacher. Ten years further back then ..........
If you mean most influential on current safety then maybe Stewart/Watkins
Most influential on design then maybe Murray/Chapman/Newey
Most influential as TP then maybe Williams/Dennis
But none of these guys (nor the hundreds not name-checked) exist in a vacuum. They all influence and are influenced by those that when before and those around them. Without any one of them, we would be in a different place. Without the guys that started it all, we might not be here at all.