I've tested Cuddeback, Moultrie, Stealth, Leaf River, Talon, Widlview, Camtrakker, Bushnell and Predator along with several homebrew style trail cameras, over 20 trail cameras total and the Predator is the fastest so far.

I know that the question is about trigger speed alone, but please don't let trigger speed be the only determining factor when you select a digital trail camera.