Hi welcome to the forums, i feed my pet parrot a selection of seed and Harrison's pellets more of the latter and omit any sunflower seeds and peanuts but add fruit and veg to the mix and a grape or pomegranate for the treats.
Some years ago pellets were believe unfit for breeding birds due to the lack of crop milk, i personally could not say if that was an old wife's tale or not, when i use to breed some 20 odd years ago i fed all my birds on a seed mix and a good selection of willow branches in the aviary which the birds destroyed in no time, i use to hang meadow grasses in clumps from the aviary roof which i collected every weekend sprayed with water and my birds loved that too.
To summarize i would say for a pet bird not intended for breeding i would feed pellets, or do as i do mix with some seed each bird owner will have their own preferences so this thread may throw up different opinions.