(pulls out keyboard collection)
I'll dig through my cache of keyboards and find the 3 worst...
Microsoft Natural - I can game on them, but typing is hard for me since I don't type "normally", my hands have to be offset a little because they are so darned big, so I'm very uncomfortable on this keyboard.
By far, the WORST PC Keyboard ever made, that is just a normal keyboard....is this one, the infamously cheesy BTC-53 series. I trashpicked one off the curb, thinking it would have Alps keyswitches, as it looked like something that would have them, being boxy and PC-like and all...nope, It's a very mushy feeling piece of junk, and unfortunately, I had to use it on my 286 till I found that 5 pin connector for the IBM Spacesaver a few years back (that was a godsend). I got another one in a lot of keyboards, it mostly vegetates in the kitchen cupboard.
And my honerable mention for modern consideration on old PC's, this awful HP Multimedia keyboard, it's like the 1990's version of the BTC! I used it on the IBM PS/2 for awhile, and it has NO feedback whatsoever, it's like somebody made a typing technology using wonder foam for the key actuators. BTC created "anti-feel" technology, and HP perpetuated it apparently.
I like my keyboards big, rectangular, chunky, and beige, like my trusty Model "M"'s, my model "F", and my Northgate Omnikey 102, those are the best I've ever had.