go with delco's as I've heard many people run into issues with the bosch one's. Not saying they won't work, but I've heard no problems with delco's and issues with Bosch sometimes. I actually replaced mine not too long ago.
I call either of these guys from this link for GM parts.
http://shbox.com/1/4th_gen_tech2.html#Dal_and_Jason
GM dealers tried to gouge me on price and new AC delcos were cheaper than in-store boschs when ordering from either of them.
-Brian