Best Dropbox like referral system for landingpages?

Many of you thought about it already I guess. What's the best referral system for landing pages at the moment according to your experience?

At the moment I am checking unbounce as landing page with "viral loops" integration. Anyone experience here? https://intercom.help/viral-loops/en/articles/2173589-the-refer-a-friend-template-tutorial

The goal is to incentivice users to generate referrals similar to dropbox (refer a friend and you get xxx for free).