I feed a large variety of food.
For the finches, I use a combination of several brands of finch/canary seed as well as pellets and egg food. They enjoy many different vegetables: romain lettuce, brocolli, chopped carrots, etc. Apple or grapes is another regular treat. They get hard boiled eggs along with the shells. Mealworms and millet are also favorites.
The other birds in my care also get appropriate seeds and pellets as well as fresh fruit and vegetables.
The variety not only helps keep them healthy, it helps keep them busy and happy.