I like that the Xaxis team works well with everyone on the team and works hard to get us what they need even if it does not involve them. They act as a resource to our team and are always ready to make great recommendations for optimizations. They are on top of financials as well and are always able to make changes on a whim.
I feel that sometimes Xaxis is not able to make deliverable deadlines due to their publishers. Whenever there is a delay though, they are always in constant communication with our team to let us know. Additionally, I believe that they don't provide as much detail in initial requests, and this is somthing that you have to pry them for.
We're solving our duplication by running all of our networks within Xaxis. They provided better targeting and by mooking all of our media across ALL publishers, we are able to better optimize on all campaigns.