This is a tricky question because it depends upon your preferences, finger size, and budget.
Generally, our customers are happiest with engagement stones around one carat. This is equally true for rough diamonds, sapphires and cut diamonds. For a slightly larger looking stone, but still within a typical size range, we suggest increasing the size to up to 1.5 carats. And, if you're looking for a stone that will wow and really pop on the finger, then we suggest a stone that is between 1.5-2.5 carats. Anything above that size stone, in our opinion, begins to be a bit unwieldy and is less useful for daily wear.