For online video ads, what is more important: views, likes, comments, or customer contact?

Depends on the campaign or client's objective, for example if the campaign objective is awareness, then views is the most important KPI in this case, on the other hand if the campaign aims to stimulate call for action then comments and customer contacts are the most important elements.. and so on.

Well, its totally depends on advertiser's primary goal. If advertiser's primary goal is to drive traffic ; views goes well with that. That's purely prospecting or branding of product. Some may drive video ads to engage the audiene and make them to take necessary actions such as like or comments. With this,  advertiser's filters their audiences..  This pool of audiences or those who atleast shown interest in seeing an ad can be targeted later to make purchase of their product. 

Comments and customer contact

Well, i think all things matter alot,instead of doing scrolling people will do like and if they are interested they will contact and do comments.