My party that I brought to endgame first time around was F/R, L/B, N/L for front line, and back line was R/M (Just for the subclassing skill points, mostly just used her as a Runemaster) and M/A.
I like runemaster on the Fortress for the rune skills, which add to defensive capabilities, and for that one passive I forgot the name of that can cancel an elemental attack on the line of the skill's owner.
Bushi on the landshark was fairly obvious: Bloodsurge for more damage. So much damage. TOO MUCH DAMAGE.
Landshark on the nightseeker... I have no clue. Maybe the def up for dual weapons skill? Yeah, that sounds likely.
Runemaster medic was, as aforementioned, just for the skill points. Pure runemaster or go home, multiclassing isn't that good for these guys.
Medic/Arcanist was for versatility, and because the circle regen thing was actually affected by the medic's healing boosting skills, making for more effective healing and various binds (My nightseeker handled status, seeing as he got stronger every time he afflicted one) all in one.
Once they all got to level 99 I retired them into their own classes, and I'm switching around builds to see what I can do with them all. I'll try using the five other classes next playthrough.