From a purely aikido centric point of view, try them all, as they all will give you different perspectives on technique. On the mat its all just about learning anyway. Additionally, if this is a technical interest of yours, you may want to look at techniques outside Aikido, as many of the best aren't part of the art. I recommend Hock Hochheim's books.
If you have the extreme bad luck to really get in such a fight, take whatever opportunities present themselves at the moment, including appeasment or running, rather than planning one technique or another. Fighting is unpredictable. Most of all, ignore any cuts and continue resolutely until you win.
I have no idea what started you on this track. Eric didn't say anything about his doing something as stupid as going trawling for a knife fight. He asked a reasonable technical question about techniques within our art.
Since, however, we have arrived at this discussion, I question your facts. You might want to read James LaFond's "The Logic of Steel" containing descriptions and statistical analysis of 250 knife attacks in Baltimore, rather than theorising.
I do, of course, agree that never getting into a knife fight is by far the best thing to do. However, despite being a peaceable old guy, I know a fair number of people who have gotten into one, so, I think it is worth considering in ones training.