I saw an interesting review on YouTube about party AI.
Essentially, set up each npc to follow themselves (i.e. not pc or other character). This way their AI best management seems to set in, and they perform well, pretty much regardless of your party composition.
That being said, I have found the you have to have a rogue (I do so miss the "lock bash" mod) in you party
If you don't play as a mage, you need one/two depending on your playstyle
I play as a mage (lightning-ice/knight enchanter), and typically take a tank, ranged rogue and second mage on all my harder stuff
For the general exploring, rifts, and side missions I switch out my second mage with a dps/ranged rogue or a dps warrior (I have 2)
It seems most (if not all) party compositions will work (on normal setting at least)