Live toons are much better then mercs anytime.
6 box group means you control the actions of everyone, instead of ye old dumbass getting your group killed. Though you might have to put a mirror near your computer so you can yell at the dumbass now and again still... --wink--
As for group make up... there are a lot of combos that work. Entirely depends on you really.
Something to tank
Something to heal
A few things to DPS
And a utility or 2 (or more DPS/tank/heal, of course)
entirely depends on what you want to get out of the group, and what you like to play, and what you plan to accomplish. I mean... group content is a lot more flexible. If you eventually want to raid with those toons, you would want to look towards what role you want to fullfill on the raid (or if your building a raid force) as opposed to being just a XP farming group, as opposed to being an item farming group, as opposed to ......
For instance Raz likes his tank/healer/wiz/wiz/wiz/wiz groups. He also likes his tank/shm (I think) /zerk/zerk/zerk/zerk group. And then he discovered BLs, and how to set them up properly... now he is having kittens!
You will get more enjoyment and fullfillment) out of picking toons you want to play, and learning them forward/backwards, then you will taking someone else's advice on what they find enjoyable, in my opinion. =)
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Sorry, long work hours has my typing screwier then usual....