I personally love my 72x Kenwood Drive. I will agree that there are faulty units out there, I had one, but hell just return it until you do get a decent one. It is the fastest and quietest drive on the market. Installing any of the windows flavors simply FLIES on this drive. I've had problems with a couple CD-R's but very few. Any that I do have problems with I just throw in my TDK veloCD and it fixes it right up. The 72x has effectively the same amount of noise as a 24x cd-rom so it's very quiet.
If you go with the Asus 50x you might as well put a jet engine in your case too. That's one of the loudest CD-Rom's I've ever heard, next to the Creative CD-Roms which are total junk.
If you have your mind set on NOT getting the Kenwood, the Toshiba 48x drive is very quiet, and extremely reliable reading all CD's including CD-R's. If I was to only have one cd-rom in my system and didn't have my cd-rw drive to read with, the Toshiba would be the one single drive I'd own, it's awesome. That would be my choice next to the Kenwood.
If you have SCSI, then without question the Plextor 40x is the drive to own. It does 38x DAE (for a 40x read drive that's incredible) and it's well worth the money, grab one.
dm