I had a pretty big Metalcore-phase back in 2007, a lot of Trivium and KSE, now my interest for the genre is pretty low, i haven't even heard the latest KSE-album.
Trivium is easily my favorite out of the two bands, i'd say Shogun and Ascendancy are the best albums, but Ember to Inferno and The Crusade are both very good as well.
As for KSE, i'd say either Alive or Just Breathing, or The End of Heartache.