There are many different types of key switches. Some require firm key presses, others are light. Some are loud, others more subtle. Some are crisp, others are smooth. My advice would be to try the different switches and figure out which one you like best. I have the following in rotation:
Buckling springs (IBM Model M)
Very LOUD, promotes a typing style where you're banging on the keyboard. Tactile, yet smooth.
Tactile and loud. Almost as loud as the buckling springs. Not as smooth as the buckling springs. Whereas the former is tactile an smooth, the white ALPS are tactile and crisp. This is because the key "gives" near the top of the travel. Buckling springs fold much later on the way down.
Technically Topre switches aren't mechanically switched. However, they do have individual springs under each key, and people who have tried them rave about them. They are SMOOTH. It's like typing on butter. You need a light touch. They are the most subtle of the bunch. Your first reaction will probably be "what's the fuss?" But there's tactility in there. They make a "toc" sound when bottoming out. Sounds glorious at speed. They aren't loud. They're extremely addictive to type on. Expensive boards though. Expect to pay around $300 for a keyboard with Topre switches.
Cherry MX Blue
Clicky, sounds a bit tiny compared to the buckling springs. Rewards a light touch. I don't like the sound - a bit high pitch for my taste.
Other Cherry MX Switches
I haven't tried the browns, reds, clears or blacks, so I don't have an opinion on them. Cherry MX switches are the most readily available and common though. Most of the new wave of mechanical keyboards that have become fashionable lately use them.
Once you've decided on the switch, other things to consider are:
- With or without numeric keypad? Maybe you are in spread sheets all day and need the num pad. Or maybe you write code all day and have no use for it. No num pad means your pointing device can be closer to your hand if you're right handed.
- Wired or wireless? If wired, maybe you'd like a built in USB hub?
- Backlighting? Maybe you like to game in the dark. Or maybe you touch type and don't care.
- PC or Mac layout? Not a biggie though. Keys can be remapped in the OS.
- Build quality and material. Will the plastic get shiny after a few months of use? Will the key caps fade?
- Dedicated media keys?
- Programmable keys?