First of all, what do you want your keyboard for?
- Writing / Coding
- Data entry
- General stuff
For a long time I used a standard UK format keyboard, then I started to get wrist pain. I got me a Logitech Comfort laser
Which was okay but had a none-standard layout of the [INS][Home][Pg Up][Del][End][Pg Dn] keys. Swapping to another keyboard at home or in the lab was a pain because my fingers didn't know how to find those keys any more.
It was a nice keyboard but it was really mushy (dome membrane). When the backspace key started squeaking, I knew its days were numbered. By this time, my IT department had started offering ergonomic keyboards so I went for a an MS Natural 4000 Keyboard.
Yuck! Even more mushy, and big. All these ergonomic keyboards are really large, take up a lot of desk space.
This is when I started reading about mechanical keyboards and the advantage of the key-switches of various types. I tried to find an ergonomic keyboard with switches, the choices are limited to the slightly weird and the downright abnormal. The biggest problem being that they have a different layout then a standard keyboard. Yeah, I don't want to learn to type all over again, even if all the alphabet keys are in the right place.
In the end I took the plunge and got a brown switch mechanical keyboard - The Filco Ninja Tenkeyless:
And.... the wrist pain didn't come back.
This is my main, work keyboard, the one I use every day. I write a lot of documents and code. It's perfect for that. The keys click, they are not too loud though.
I chose a keyboard without the number pad because I never had reason to use it on every other keyboard I ever had. My fingers know where the numbers and symbols are on a normal board anyway. It was a waste of space, and without it I can have the mouse nearer my left hand (should I choose to use it) which is another ergonomic benefit.
Now, if you do data entry or a lot of gaming a number pad is more important.
At the time, there weren't a lot of gaming keyboards that had mechanical keys but its a different story now. Next time, I think I might pick up a mechanical gaming keyboard, because a) they have mechanical keys, b) they look damn cool c) they are cheaper than vanilla mechanical keyboards - this last is my own generalisation but they seem to be about 20 to 30% cheaper on the whole.
Your milage may vary.