Just returned from 2 weeks in Fiji - our 10th visit - but our first to these two resorts. We chose the 2 resorts (rather than our usual preference for tiny resorts like Navini) as we were taking our 16 year-old son with us and he wanted somewhere we're there would be more to do.
TOKORIKI - we've now stayed in all of the small and mid-sized resorts in the Mamanuca group and I'd rate Tokoriki as by far and away the best of the mid-sized resorts. Excellant bures (29) within a really well layed out resort. All bures are beach-front, well seperated and private, have king-sized beds + a seperate area with day-beds and nice extras like a coffee maker. The beach is good with lots of lovely white sand and the pool a reasonable size. The food is the best I've had in Fiji - apart from at the really 5* resorts (yasawa/vatulale etc) and as always - wonderful and friendly staff. The dive operation is first rate for both beginners and those more experienced (even though the best diving is not in the Mamanucas). One slight dissapointment is that there is no snorkelling off the beach (the reef is some way out) but they take a boat out for snorkelling each day. It was Aust & NZ school holidays while we were there and they arranged lots of activities for the kids. There was a mix of Australians, NZ's, Americans (mainly honeymooners) and a few Europeans there. We took the sea-plane both ways and I'd highly recommend it rather than the boat transfer from nadi (3 1/2 hours by boat v 17 mins by plane!).
SONASALI - this is by far the biggest resort we've ever stayed at - and I would never ever go back. It is huge (much bigger than they advertise) as they've added at least another 20 bures - so there's around 70 as well as the hotel-style rooms. The resort is built on a mud-island about 100meters off the mainland and a large rock breakwater seperates you from the muddy water and black sand. They've imported acres of white sand (which is okay) but it is a very faux "beach" experience. They do have a large pool, but as no one can lie on the beach it is always really busy around it. The dining is a bun-fight every night - you must book and the service and food quality is very erratic. The food was generally poor (a lot is pre-cooked and then reheated) and several people we spoke to had had tummy upsets. You have to book around 1-2 days ahead for most of the activities and pay extra for many of them. They play exceedingly loud music all day (at one point there were 3 different sound systems going at once) and have an even louder band every night. If you're travelling to Fiji to enjoy "Fiji" rather than just stay in a resort that could be anywhere - don't bother.
I guess the entire trip just confirmed to us that if you want to really get the most out of a visit to Fiji you need to go out to one of the islands. Spend a day in Nadi (1/2 a day is really all you need) but then head out to the smallest resort you can!