BTW Influence is also determined by the number of followers (whether they were talmidim in yeshiva or not) they have and how strongly they follow the guidance of their leader.
Some of the names listed by other posters may be big talmidei chachachmim and given nice shiurim but few followers after they leave the shiur.
In some yeshivos a maggid shiur may have more influence on the present and past talmidim than the Rosh Yeshiva