+10 agility gem or +20 attack power gem is better for dps?

i know that +10 agility = +10 ap and also helps with crit rating.

just wondering is it more worthwhile to get the crit rating or should i just get the raw attack power boost?

i'm gonna gem 5 of them. so i won't mind mixing both unless someone could pin point out the clear-cut better gem here.

if you are after sustained dps, ie not tanking, then i would suggest the AP spinels (maybe 3 AP ones and 2 agil).
On the other hand if tanking , the 50 extra agil adds up to A LOT of Crit, dodge, and armour!