Hi, It depends on the results you're getting from the website/network and the specific campaign. If your test campaign is showing more impressions and less clicks then you may want to advertise based on PPC. if your getting a lot of clicks then you may want to get a CPM deal. In general, I would say that CPM is better for branding/popularity. and PPC is better for results ( sales, commissions etc ).
Depend from yours budget. You can inform clients that you exist by using CPM ads, but I think the real effect will give CPC ads.