Examining wearing of my notebook keybord, comparing with dirtiness of my workstation kyebord, weighting the areas of keys, ehmmm..., it is...
space, e and i in this order.
Comment on Re: The most useful key on my keyboard is:
If I were you, I'd compare with the cleanliness of the keys, not how dirty they are - space, shift, control and friends are all sparkly clean but the numpad is showing its grime.