On weapon enchants: Mongoose is currently considered the only viable weapon enchant for rogues. 20 agility is inferior, even on the offhand. Executioner was once thought to out-scale Mongoose as a main hand enchant towards the end of T6 content, when the rogue obtained a decent amount of passive armor penetration. However, this observation was based on a bugged model. The circumstances under which Executioner does out-scale Mongoose are now thought to be so restrictive as to rule out use of the enchant for PvE purposes.
Taken from the Roguecraft 101 thread from Elitist Jerks.
http://elitistjerks.com/f31/t16940-roguecraft_101_a/