Which one is better? 

Simply put: NEITHER.

Lab grown diamonds and natural diamonds are composed of the same chemical make up, have the same hardness, are both judged by the 4 Cs, and are indiscernible from one another without precision machinery.  

What it comes down to is a matter of preference.

Which should I prefer? 

Yes, this is what many people think when choosing between the two.  If I offered you a choice of two Mercedes that were identical, with one costing around 35% less than the other, you would have an easy choice right?  

With diamonds though, even when all things are physically equal, the history and source play a role in the stone's value. 

An earth grown, natural diamond has developed naturally over a long period of time, and gets a higher value attributed to it due to its perceived rarity.  Since natural diamonds are limited in quantity, whereas lab grown can be created to any extent, natural diamonds are currently holding a higher market value.  

So natural it is then? 

Not so fast, the demand and acceptance of lab grown diamonds is increasing.  Lab grown diamonds do not have a history of poor ethics or questionable sourcing.  Although with most natural diamond suppliers participating in the Kimberly Process today, the ethical issues from what you see reported, are rare.  

What lab grown diamonds do best, is that they bridge the gap between desire and affordability.

Costing roughly 35% less than that of their natural peers, for the same physical stone, your dream ring becomes more attainable, while still leaving money for the honeymoon.