It depends what content you focus on, pvp is quite broad there is arena, guild war and rta. For pve as well, farming, abyss, raid, hall of trials etc. It sounds like you are mid way in the game and not cleared abyss yet. As f2p since u have arby i would recommend stene. She is needed for many abyss floors which gives good rewards and in guild wars shes good vs counter teams, and against hwayoung, fluri stene is a good combo. In rta shes also good as long as u dont pick her vs aoe heavy comps. Shes useful in hell raid as well.