Buckle is definitely quieter putting on and off and does not make the scratching sound when you draw the bow.
If you shoot with a loop they you should really try one of the newer hook style releases out today. They are wonderful to use with a loop. No more having to look at the loop to make sure it is hooked up properly, gives a cleaner release than caliper style releases, much less wear on the loop.
I have been using a Scott silverhorn for three years now and will not go back to a caliper style release though I do still keep my sabertooth as a back up.
The Rhino XT which is another excellent choice from Scott.
Tru Fire makes the hardcore which self centers to the pressure applied to the hook.
TruBall makes a couple nice ones as well... the beast and beast II.
Spott Hogg wiseguy
Carter Rx1.