what is the best way to track marketing campaign in mixpanel

@Tomricco you can use all the reports for this, here’s an overview of each of them:

• Insights - for questions like 'how-often?' or 'how-many?' or 'when?' and also 'what?' (it's the swiss-army-knife report really…)
• Funnels - to see time to value ( down to the minute), conversion rates, frequency, drop offs, structured user journeys and more
• Flows - to see natural user journeys to, from and between specific events
• Retention - to analyse your user's repeat behaviour, can even breakdown by channel or any other property
• Cohort - segmenting your users by their action and/or inaction, the land of the power and dormant users
• Signal - The place to figure out the events that lead to the aforementioned segmentation for better or worse
• Impact - Answers the question 'did it work?' around anything new
• Experiments - Shows you the differences between 2 user segments across a whole list of KPIs

You also want to look at a few things specifically:

• UTM parameters to track attribution 
• Create cohorts from funnels to track the retention and onwards behaviour of those converted and/or those who have dropped off
• Comparison events, for any A/B tests in campaigns you can see which path converted higher

There’s also a post with some more ideas here.