Let me preface this by saying that I'm not a millisecond junkie like a lot of people. All three of these drives rock, from the reviews I've read, and ANY would be a great purchase.
That said: Read the review at CDRInfo.com comparing these three drives, and you'll see that the TDK and Plextor are NOT "the same drive." They deliver very different performance ratings in a number of applications. (Note that on some copy protected discs, the Yamaha kicks both their butts.)
The CDRInfo review notes that the Yamaha rarely achieves 16X, and the TDK only achieves it after a lengthy rampup (so, "as fast as 16x."
Now, if you hadn't guessed...

I own the Plextor. Aside from a strange conflict with my ATA/100 controller that I can't figure out, I lvoe the drive. I've burned a dozen CDs so far, and it's fantastic.
It also has amazing audio ripping speed. This is something the TDK plays up heavily. Again, according to CDRInfo, the Plextor wins that contest hands down.
But back to where I started this note: I don't think ANY of these drives are worth $100 more than the other, so don't buy a Plextor just to buy a Plextor. If it hadn't been tax refund time, I probably wouldn't have.