Well, i’m far from crucible expert (i don’t really like it anyway) so take my words accordingly.
First off, threat / aggro control is nearly non-existent in GD so you BOTH have to go TANKY enough.
In a case of tank + glass cannon combo the mobs would ignore the low dps tank and go after the glass cannon and skills like War Cry would only mitigate this problem a little bit but wouldn’t solve it in the long run.
To complement each other, there are two things to care about:
- Buffs and debuffs.
Going different class combos (for avoiding skill overlap cuz the same buffs / debuffs won’t stack) is obviously a good idea, but sharing damage types is also welcome so you can both utilize the buffs and resist reduction debuffs of each other.
- Single target an AoE dps.
For crucible you need to be good at both as there’s very high mob density AND regular (mostly multiple) boss spawns.
Since you’ll be going as a duo you have the advantage of freedom to be more focused.
One of you could specialize in single target dps, preferably melee (S&B physical witchblade / commando are still good choices) and the other could go for a tanky caster build (BWC sorc, SJ ele, DEE wh (well, not that tanky essentially but can be adjusted accordingly), CT sorc, you name it) for massive AoE mayhem.
Those casters mentioned have solid single target dps too to support the melee guy against bosses.
Personally i would pair the sorcerer/elementalist with the witchblade, or the wich hunter with the commando for the different buffs/debuffs (but going 2 demo or occultist class has some merits too as you can spare some skill points by not taking some skills what would be pretty mandatory otherwise for a solo build, and cadence soldiers are notoriously starving on skill points :)).
Of course these are just examples, the possibilities are way more diverse in GD (less so in crucible but still :)).
And i know a told you before but i can’t stress enough that PERSONAL SURVIVABILITY is KEY in crucible.
P.S.: sorry for the bracket-fest, complex sentences are prevalent in my native language.