The armor is for all game modes, not just PvP. The different factions depend on the bonuses you want to have for your Guardian. Vanguard is basic armor. Each of the factions is more of a specialization for your build. Dead Orbit > Melee and Grenades New Monarchy> Super and Melee Future War Cult> Grenades and Super You do not have to do PvP in order to get the Crucible marks. You can just turn in extra materials to the Quartermaster for marks. 5 Marks, 200 Glimmer, and Reputation for each material trade, same for the Vanguard Quartermaster.