I assume you're new to the game. The 24-man raids come with the .1, .3, and .5 patches with the 8 man trial "raids" happening in initial, .2, and .4. The hardest content in the game, however, is Savage versions of the 8 man content. If you wonder why that is, you'd had to have been there for the likes of World of Darkness and Weeping City of Mhach when new.