Loose seed mixes are frankly terrible for parrots of all sizes. They pick out and eat only the tastiest bits, and throw the rest on the floor -- meaning that their "balanced" diet becomes anything but. If your budgie will accept pellets, those are always the best option. However, if your bird is a picky little thing like most budgies, look for a clustered seed mix instead of a loose one, because it's harder for them to be selective about which bits they eat when it's all stuck together. An example would be Lafeber Nutri-Berries, which is what I feed my own birds. Another advantage to Nutri-Berries is that the seeds are pre-hulled, so any added vitamins actually get eaten with the seeds instead of discarded with the shells.