Really, it entirely depends on your ads and what follows afterwards. If your sales funnel is especially effective, but your ad isn’t very good, CPC is definitely the way to go. The guaranteed clicks put people into your funnel, and the funnel does a great job of converting those people into customers, so you make a lot of profit. There are plenty of examples of this online, so definitely do your research.
On the other hand, if your ad is very good but your sales funnel isn’t quite as effective, you end up with a situation where CPM is better. CPM funnels as many clicks as possible into your funnel, and your funnel converts people at whatever rate it works. You need as many opportunities as possible, so you have as many chances to convert as possible. So if you think your sales funnel isn’t effective, go down this route.