This is sort of our standard policy:
Realistically I wouldn’t use AdRoll outside of Facebook unless AdRoll really came up with some great creatives, which I have yet to see. Have never seen good results using their non-FB retargeting.
My response is that I try to stay away from Cost-Per-Milli bidding whenever possible, and using Google, we bid using Cost-Per-Click and have a ton more tools and levers at our disposal to optimize ROI (Site placements/exclusions, dynamic text ads, display text ads, geo-targeting/bidding, day parting, demographic bid modification, site-based topic-based targeting, jargon, jargon , etc). Clients love hearing that. On AdRoll, there isn’t much we can do from a management standpoint aside from ad testing and weekly budget adjustments and very rudimentary geo-targeting.
The only reason we still even use AdRoll for Facebook is that Facebook itself doesn’t offer dynamic/liquid retargeting yet through their own platform. The benefit AdRoll has is that you get visibility in display networks other than Google, plus you can run Facebook retargeting in the same account. It was overall good and easy to manage, but we stopped running it since it was more costly (CPM and CPC) than our Google retargeting.
CPC > CPM when ROI is a concern
AdWords > AdRoll
Use Google retargeting for web display, use AdRoll for FB
AdSilly 