My lovebirds like Hagen tropican. I give them Psittacus when I can't get hagen, and recently I found some zupreem natural on a sweet deal and they took to that so I went back for another 4 kilos.
But really, it is as Mizzely said above, any pellet they eat is fine. The unfortunate part is trying them all to see which they like.
Just offer small amounts in the bowl as to lessen waste, I toss out pellets daily to keep them fresh.
My birds don't really like fruit, one pair loves strawberries, and another likes orange, but mainly I feed veggies. Peas are a hit in our house. They also enjoy peppers very much, I usually offer long green italian peppers, and large red bell peppers. Try offering finely diced, as mash, in large pieces, as well as whole (washed with stalk removed) and see which they are more interested in.
Sprinkling a pinch of seed on top of veggies can also help to get them interested. Even if giving a piece of veg, you can wet it under the tap then sprinkle the seeds on so they stick.