What is better to use for baking in an incentivized viral loop into my website, having users "share" on social media or using a "referral" system?

I'm trying to see what would be better to bake-in to my website to create a incentivized viral loop. If I just add a simple "share" feature it makes it easy to just share a message and I would have to give them their incentive for doing this immediately, but then how do I actually verify/control that they are sharing to actual friends or didn't set up a fake social media account to share on...less friction immediate reward. On the other hand, with a "referral" system I have more control over who is actually signing up based on the unique referral ID I provide to my customer and I could give them their incentive after the user signs up. However, I feel less people would be willing to do this because the incentive is not immediate....more friction delayed reward.