I believe most team runs are at Class-Dice, that decreases the chance of getting the unique, since you will only get it, when its your class. yes you can be lucky, but I think you can't do enough runs to be on the average chance.
If you run solo, you can keep the item if it is not on your class, and you see alot of people trying to trade item for class X to their own class. There it is obvious that these are from solo runs.
Since the drop in team is allways more plentiful, you have a higher chance on an unique to drop in one team run compared to one solo run.
But its up to your self if you get more items and more chances when beeing in single run or in team run.