Firstly, Vertoz seems publisher-oriented though it has services for both publishers and advertisers. This can be confirmed if we get a breakup of revenues between publishers and advertisers.
Most of the publishers initially go through the thought of Google’s AdSense vs. Not AdSense. Publishers who get AdSense service will stick to it and then think about using other platforms like Vertoz to further increase their revenues. Found in one of the sources below that both AdSense and Vertoz can coexist in a website.
Publishers who don’t get approved to Google’s AdSense choose other Ad Networks like Vertoz. Apparently, they don’t get AdSense because it is very strict and also takes a while to get the approval completed. On the other hand, Vertoz’s approval is instant and they check it later.
Most of Vertoz’s customers are apparently publishers who get rejected by Google’s AdSense 
Monetisation: There is nothing in the market which beats AdSense and Vertoz or other ad networks fall behind.
Customer Support: Vertoz seems to be better in this regard.
For advertisers, Vertoz is cheaper and more targeted but Google’s AdWords gives more ROI and more quality traffic to advertisers due to quality traffic from Google’s AdSense.
Disclosure: Above information is based on my interpretation of info in below sources. Please note that there is some contradictory info across the sources presented below. Not a buy / sell recommendation. No holdings in Vertoz.
Sources for learning:
https://tophostingnet.com/vertoz-review.html