So I have experience playing with both the K70 and Blackwidow keyboards.
[strike]K70[/strike] Strafe - Keyboard is pretty nice, comes with some additional keys (replacing WASD or QWER depending on what games you play). In terms of the action on the keys, they don't feel like they have any weight/resistance to them (very easy to press). The keys on this keyboard are quieter than the blackwidow.
Blackwidow - Unless they changed the package contents, the blackwidow doesn't come with spare keys. The keys feel weightier than the [strike]K70[/strike] Strafe's keys, but this is partially due to the keys being louder. It's still pretty easy to use though, I used mine for a solid two years with no complaints.
If I had to re-buy one, I'd probably go for the [strike]K70[/strike] Strafe. I like the fact that they come with the bonus keys - helps you feel your way around the keyboard better without looking.
Edit: Actually it might have been the Strafe not the K70. From the images (of the replacement keys) it might have been the Strafe.
Edit2: Yeah my bad it was the strafe not the K70. Get the Strafe!