[throwaway675309]

It actually depends. The type of keyboard is not necessarily as important as the manner in which you depress the keys. RSI is usually caused by performing an action that isolates a muscular movement.

So for example, you might have a mechanical keyboard which may have a longer vertical travel, but if you depress the keys through the usage of the weight of the arm and let gravity do some of the work, you might be able to ameliorate some of the potential causes of RSI.

Source: studied ergonomics including the Alexander technique and Taubman for piano, some of which applies to computer keyboards.