From my own experience I've found that you always have to spend at least $5 on each FB advertising method (with different campaigns) to see which one brings the best results for the particular thing your promoting then focus on making that one campaign even better and put more cash on it.
But your advertising method should be focused on what you're promoting. For instance, if you're promoting a valuable blog post (or reverse squeeze page) then it makes more sense to use "post engagement" instead of CPC. If your content is really good then you'll get more shares and likes which will automatically get you cheap clicks (less than $0.07) and organic traffic from all the shares.
If you're promoting a squeeze page then test both "post engagement" and "cpc" then after stick with one that brings you the best results.
It's all about split testing, there's no one size fits all. You have to be hands-on and do all the legwork.