I'm not familiar with AG, but that is a nice looking bike. I don't like the frame geometry on the Kestral at all, looks more like a TT frame to me.. Shimano 105 and Sram rival are the 3rd group down the scale for both companies and either would perform great.
I'm not a Sram fan, but with those 2 choices I would go with the AG if it were me..
Just my .02....