1) Better Results A few weeks ago, I wrote a post describing the differences between AdRoll and Perfect Audience in terms of performance. Both performed well, but PA performed better, and for less cost.
2) Clearer Billing Practices One thing that frustrated me about AdRoll was their vague billing methods, especially when you are running multiple campaigns for multiple customers. AdRoll would build up a "reseve" in our account, even though the campaigns weren't exhausting it. Perfect Audience sends a very clear, detailed summary of the billing each week by campaign, showing what was used the prior week, and what they need to replenish the campaign to get it to the weekly amount.
3) Easier UI Both systems have similar UI in terms of the setup, but PA is the winner here. I like their UTM tag builder, and the way I can differentiate between clients in what I would call "agency mode."
4) Receptive to Customers I thought that PA did a fantastic job of reaching out to customers and getting feedback. I gave them a few ideas that seemed to get their interest, and I like dealing with companies who value my opinion.
As I said earlier, both systems are great platforms, but I prefer to use Perfect Audience for the reasons above.