You will want: Warrior (guard and 2-hand for keep doors), sm or chanter (ml9 pet eventually +pbae), and a spec buffer (shaman would be my choice, endo + sexy rr5 ability). For your 4th toon you could go warden (extra heals and celerity) or bard ( speed 6 for less downtime, heals, endo).

 

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4 is an odd number, you dont add much to your group compared to 3. if you can kick up to 6 the power of your group will go through the roof compared to 4.

i think id go with bard over warden for a 4th. you will probably want both tbh, but a majority of the time having the bard run speed and the ml ability to port around your group is nice. the power regen and big group heals are nice too.

edit: but if you can run 3 minimum then everything is going to be easy.

tbh i never could getthe hold of a warrior for argo.

i went pally/chanter/sham/warden

pally for chanter block and argo control
chanter for ml9 focus pull and pbaoe
sham for buffs/decen heals and rr5
warden for cross guard/sham gurd and pbt and heal font

 

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If it is a shared zone like the laby just make a toon from the realm you want the loot from the group leader. Like if you want the friar staff from the spirit guardian make an alb leader, if you want the mid slash version of moment of zen then a mid leader will procure your desire. Same goes for any shared zones, like ToA, and NF, etc etc. Even RoG depends on the group leader. If you want arcanite a hiblet leader is the way to go, but if you need some arcanium salvage gear alb or mid will do.