As a travel agent (specializing in honeymoons) I travel to different destinations to become familiar with the product that I am I selling. Of course, this also also has allowed me to dive in these destinations as well. I have been to Fiji twice and traveled through the island groups. Although I have not been to Lalati, I have been to Qamea and logged about 10-15 of my dives from that property alone.
Fiji is known as the "Soft Coral Capitol of the World" as you may know...these soft corals are most prolific in the warmer currents found in the Northeast, where Qamea is located. In my opinion, this "tips the scale" toward Qamea. The Somosomo Straight and Rainbow Reef are world renown, as is the Great White Wall.
The dive operation at Qamea is PADI 5-STAR, 2 dive instructors and a marine biologist on staff. Excellent equipment and a new dive boat just last year!
Although I am not familiar with the dive operation at Lalati specifically, I would be able to compare and contrast the properties and facilities, if that is important to you. Lalati is a 3-3.5 star resort, while Qamea is definitely more luxurious (4.5-star).