By using the right companion combo we can get a good buff to our damage. 
In my opinion, the best companion set to use in module 14 is:


Summoned: Chultan Tiger 
This Companion is 2 in 1. Its a 5% damage buff for 25 sec and a 10% Debuff. For the debuff to have 100% uptime you need to have Combat  Advantage otherwise it drops to 50%. It uses 2 x rings and necklace and with the new 2 offensive slot rings it can help a lot higher damage.  

Active companions:
For active companions, we need the ones that will offer the most buff in boss situations. In any dungeon, the most damage comes from the bosses and this is our main focus. To be honest now with the new loadouts affecting companions and insignia, this is less of a problem. So what are the best ones to use?

Air Archon, Earth Archon, and Fire Archon.
The bonus got fixed back in mod 12 and now they buff each other's damage. So instead of 5%, 6% and 7% we now get 6%, 7% and 8% ( below 50% HP) if we have all 3 and since buffs are multiplicative to each other we get 1.06 x 1.07 x (1.08/2) = 17.9% More damage for us. 
Razorwood.
A module 14 addition. It gives 25% Combat advantage damage and 2,5% Critical Severity.  
Siege Master.  
Siege is all around good companion. It gives 4% buff.  In Aoe loadouts it should be used instead of Fire Archon.  

There are some other companions that can be better in some situations like the boar if you always run with a GF or Batiri for bosses instead of fire archon but each one has its own drawbacks too. I want to think that after a point if one is running premade groups they would know what is better for their situation.