Depends on the bird
If they were brought up on seeds, they may refuse to eat pellets.
I give most of my birds pellets, Zupreem, both the colored fruit flavored and natural. I am switching over to the natural, cuz the fruit flavored one results in colored poop. The colored poop stains the perches.
I give one of my breeding finches LaFebers finch pellets.
I decided to switch them to pellets cuz of a few things.
#1 is waste. They eat what they want to eat, and would not eat half the stuff in the seeds (dark seeds and pellets). So the seeds end up 2x more expensive. Also if you buy "fortified" seed mix, if they don't eat the pellets in the seed mix, you are throwing away the "fortification."
#2 is mess. The seed hulls get all over the place, on the floor several feet from the cages. Seed guards work only to a point.
#3 keep them eating. When they eat seeds, they leave seed hulls on top of the seeds. After a while the whole top layer is seed hulls. They do not dig thru the hulls to get to the fresh seeds, so they stop eating.

With pellets there is no hull, they eat the whole pellet.
Converting seed eaters to eat pellets is a challenge, who will win, you or the bird? Some birds will easily switch over, some will refuse to eat pellets until you practically starve them, and the rest are in-between.
I used a technique that I read here
http://www.finchinfo.com/diet/introducing_new_foods.php
- The night before, I remove the seeds, leaving only pellets in their cage.
- - This way they only have pellets to eat when they wake up.
- In the morning, I wait before putting the seeds back.
- - First 1hr, then 2hrs, then 3hrs, then 4hrs. Every few days increasing the wait time. Usually they are eating pellets before the 4hr point.
- When I see that all the birds are eating pellets, then I stop putting the seeds back.
- However, I will give them seeds as a "treat" once a week or so.
After the pellet conversion. Most of the birds will eat both seeds and pellets, even when both are available. Others will eat only seeds, if given a choice.
Now, as to who gets seeds:
- Gouldians
- Societies who are fostering gouldian chicks.
- Parents/fosters who have chicks (hatchlings/nestlings/fledglings) to feed. Seeds are easier to regurgitate to the chicks than pellets.
- Fledglings get a dish of soaked seeds.