Just answered your other question regards Google DisplayNetwork, and I'm coming at this from an agency perspective;
There isn't a one-size-fits-all answer to your question. For some sectors, an image ad will do the job, others a carousel ad, and others a video ad may outperform everything else. Exactly as with my answer on Google Ads, it all boils down to data, and improving the ads/campaigns based on data.
With a lead gen campaign, on Facebook we would normally try a few different approaches alongside each other;
For example
Ads landing the user on a specific page of your site
Ads to encourage a Facebook msg
Ads to encourage a Facebook Lead Generation form completion
Within each campaign we will have a couple of styles of Ad....single image, carousel, and perhaps depending on budget a video.
We will then target an initial audience.
As users/click/engage/convert we gather what will be THE most valuable asset in your campaign....data.
For example...after running for a week we may quickly find out that ads are converting better for the 30-40 bracket, and the campaign can be adjusted accordingly.
We might also find a video ad converts better than an image ad.
In a rolling basis it's a case of removing the weak, and replacing with something stronger, in order to drive up the conversion rate week on week.
Obviously it does also come down to budget, as you dont want to split your campaign into parts which are so small your data is not big enough to make judgments on.
To answer your question....Facebook Ads are delivered to people, and in any business people make decisions. They will work better in some sectors than others, but it is always worth having data before making that call.
