I've used many a Macintosh keyboard since 1986, but there's maybe about four that I've really used with any regularity. As with any object you use a lot and have the occassion to try different brands when your old one wears out — not unlike automobiles — you tend to form opinions about which one(s) you think are the best.
First, the newest keyboard in the bunch, the Apple Pro Keyboard. A great improvement over the preceeding iMac/G3 keyboard (just as the accompanying Apple Pro Mouse was a return to reason after the disaster that was the Hockey Puck Mouse), this one is sturdy, roomy and… well that's about all I have to recommend it. It's quiet, which some people seem to prefer, but that also means it's really a rubbery contact keyboard with hard keys sitting on top of it. It's mush. The flip-flip tilt adjustment mechanism is pretty clever, but… still mush.
Next up is the Apple Extended Keyboard II. You'll notice I skipped over the Apple Design Keyboard with came with the 8600/9600 and beige G3 series Macs. That one was mush too. This one, however, was pretty decent. It had a pretty good feel and decent audible feedback. It was however, quieter than the original Apple Extended Keyboard, which makes it a close second in terms of usability for me. I'm a big fan of the audible feedback. This one, though, did have a clever little slider on the back which extended a riser bar out of the bottom rear of the keyboard, causing it to tilt to your preferred angle.
Now, a minor side note: The Apple Keyboard II. The AK2 was a non-extended model (no function keys, no home, end, page up, page down, etc.) that shipped with the Color Classic, the first Mac I ever owned. I bought it in early 1994, as I recall, and returned it a scant month later when I realized I had racked up quite a bit of debt for some reason. That Color Classic still holds a fond place in my heart, and I have another one today, displayed mostly just as a work of art on top of the bookshelf in my den. It does still boot up though, just in case anyone wants to play Indy or Loom or Shufflepuck or something. [Aside, you can now play Indy in your browser on the Internet Archive. — Ed. 2015-08-13]
The pièce de résistance is the one, the only, the AEK: The Apple Extended Keyboard. I really, really love the tactile and audible feedback of the original Extended Keyboard for typing, and I use it with a Griffin iMate ADB-to-USB adapter on whatever machine I'm on. I write a lot, and I'm afraid I'll eventually break one (or at least wear out the springs), so every once in a while I take a look on eBay, and see if I can grab another spare. I wouldn't be so worried, but all of the places online that sell old Mac stuff all only seem to have the AEK2 which is— again— a close second in feel, but not close enough for my tastes.
Yes, I have tried other USB keyboards, and none even come close to the solidity and feedback of the AEK or even the AEK2. I once found one that came close in feel, but it wasn't built as solid and the banging noise was something terrible. There is, though, a new keyboard from Matias (they just sent the press release out five days ago), which they say recreates the exact feel of the AEK, but it's USB and matches the finish of the newer machines (instead of beige). I'll probably try one out, but at ninety-nine bucks a pop, it seems like going after used AEKs on eBay is a much cheaper solution in the long run. [Update: The price has gone up to $149, but I'm typing this on a Tactile Pro right now. The clackity on this keyboard has a harsh, somewhat ringing sound compared to the AEK2, though, so I still keep on the lookout for good used ones. — Ed. 2015-08-13]