i usually keep my opinions hidden in nonsense or posting the exact opposite directly after one of my posts...but here's my experience. (your mileage may vary of course.)
i ran gch nightly with 2 other mages since ch4 launched...i had crit set (raksha, ifur..etc) one had vahtos and the other one didnt speak english, so i never knew who it was really. but the results in gch were clear, consistent and striking. crit set hands downs was better (and feet down, and whatever else)
BUT i think diminishing returns kicks you at around ~65% crit unbuffed...much on top is nice, but averages out it seems to no real gain.
adding 15% dmg to a 300k flame crit is nice (to a 120k flame non crit, meh, (but now after-gcd + mage present = 500k crits whic is REALLY schweet

), but critting double what one set gives blows away any thought of which is more valuable. for gch anyways..
juggler essentially combines the dmg % buff with a VERY nice crit set. aoth is 8% dmg + 8% int plus crit...aoth i think wins for gch anyways because the mdef of the bosses is reachable after you're gch geared. (especially for lazy m/w's who instead of re-statting pop berserk

)
availability...ugh. juggs, ugh. aoth, ugh. hell i hate RT so much, ugh^2. new stuff is appealing.