The agility+3% crit.
http://www.wowhead.com/?item=41398
Reason isn't because I believe agility is better than crit rating, because it isn't.
But the requirements allow you to gain better stats.
If you get the crit rating one you need 2 blue gems, so you end up gemming stamina twice.
The agility one requires one of each, the red one is automatically covered, but you only have to gem stamina(blue) once, and you're allowed to gem crit rating(yellow) instead of the second stamina normally required.
The total crit gained from..
Crit one:
21 crit(0.46% crit).
Agility one:
21 agility(0.34% crit), 10 crit(0.22% crit). -> 0.56%.
So the overall gain is greater if you gem the agility one over the crit rating one, even if crit rating is better than agility.