I don’t have lovebirds but I feed TOPs (small size), Harrison’s (Adult Lifetime Fine), and Roudybush (Crumbles/Nibbles). Colored or artificially flavored pellets like Zupreem Fruit Blend aren’t the healthiest but some birds will only eat them. Zupreem also has a Natural pellet that isn’t colored or flavored, which is a good alternative to the Fruit Blend.
My conures eat TOPS (small size), Zupreem natural, and a little bit of Zupreem fruity as treats and in foraging toys. I tried Harrison’s, Roudybush and Goldenobles as well, but had difficulty getting them to eat those. I think they just have their individual preferences - I just chose the best foods that I could actually get them to eat. Mine also eat a lot of chop, and seem to prefer it to pellets. I leave pellets in their cage all the time for grazing.
Harrison's Bird Foods
I feed Harrison's, supplemented by fresh healthy treats. My first, and later, my current avian vet recommended it. My bird loves the pellets now, but to get him converted, my avian vet suggested putting pellets out all day, and putting seeds (his old diet) out for two 15-minute periods a day. That would sustain him but leave him hungry enough to try new stuff. I presume the same technique could be used to get him to eat other healthy stuff, like fruits and vegetables! My guy was eating pellets in a couple of days, and now I can feed a good variety of other stuff, knowing he has the pellets as a basic. Pellets are out all day... fresh treats a few times a day. I also like Harrison's via mail because I never have to worry about out-of-date products.
Another couple of ideas...
My ol' man is an athlete and health nut. He actually EATS all the good stuff, so it's always around. I find that tossing various stuff into the food bowls at random is good... the variations and differences seem to stimulate curiosity and attention.
The other idea... if you can stand it (lol) EAT the stuff in front of the birds, yes. That encourages them. I have also found that if my ol' man eats stuff in front of the bird, the bird WANTS it for himself. Kinda a rivalry thing!