Good Impressions / Results Ratio (Landing Page visitor)..?

I’ve been wondering if i ever heard John talk about reach / impression and link click (and there’s two kind of counters in facebook ad)

conversion pixel that you customize to track results like landing page visitor

and using link clicks inside the Facebook platform (any action counts - likes, share, comment, etc)

Which one works best for the objective selected?

Also, How much impact does Ads Objective do on ads? for example, using Objective Traffic vs Custom Conversion (using landing page for firing Facebook pixel)

Any help is appreciated!