False modesty aside, I am a very good public speaker. Doing debate in high school, I had an undefeated regular season, as in not losing a single round. I say this just to point out that I'm not a mediocre public speaker championing the written word.

Paul Graham is right, but it depends more on context than he suggests:

Speaking about a technical subject, you want to communicate the ideas themselves. The emotional content in this case is noise. Paul suggests in the notes that academic talks are more immune to this, but having been to quite a few academic talks and given a few myself, I still find them quite inferior to written papers and one-on-one conversations. True, people can still inject the emotional appeals in papers or conversations, but they tend to get more easily noticed and filtered by the reader or listener without the spellbound effect.

Political debates are perhaps an exception. When you watch a presidential debate, you're not only looking for the president with the best ideas, but a president you believe has the leadership capacity to carry them out. You might personally want the president who has the best ideas, regardless of how charming they appear on camera, but like it or not, a lot of that leadership rests on personal charisma.