It's hard to pick one—they're both so smart. In order to manage this dilemma, the Saussure vs. Peirce Reading Group got together twice a week to hold formal parliamentary-style debates about which man was more the father of twentieth-century linguistics. Although these debates could get heated—and, in fact, the argument was never conclusively solved—participants always had fun. The group would be immediately dispersed if the debate dissolved into America vs. France name-calling pettiness.
No one denied that Charles was seriously important to linguistics, but he was more of a pragmatist than a structural linguist. He had some intense science training—in chemistry, of all things—so he often tried to invoke that credential to seem more serious than Saussure. That stung a little.
One of the biggest sticking points was that he believed that language started as a triad and went on from there; Saussure saw a dyad and that was it.
The Peirce Arrow or the Saussurean dyad? Only an expert could mediate this debate. The Peirce arrow—a.k.a. the Quine dagger—stands for "either… or," whereas all of the cool graphics for signifier/signified show a word and the thing it represents, separated by a bar. That's why they called in this Harvard Symbologist. Some people thought he was a little New Age, but they trusted that he was the only one who could settle the dispute about which symbol was cooler once and for all.
Who better than this sensitive and intelligent interdisciplinary philosopher to offer unsolicited tidbits about the equal importance of science and the humanities? Although she often found herself talking as if to a group of pre-schoolers, Nussbaum was able to make folks from the hard sciences and social sciences feel equally accepted and important.