As to brands - Harrison's seems to be about the best, and was the one recommended by our avian vet: it is expensive, but it's fully organic and doesn't contain any added sugars, colours or flavourings. We give Isis the 'Lifetime complete course' and she *loves* it - she even used to pick out the Harrison's in preference to the sunflower when we first mixed the two to ween her off the seed.
(http://www.24parrot.com/Harrisons-Adult-Lifetime-Coarse--Complete-Parrot-Food-P5805a/)
If you're after something cheaper, we've found that Optibird is also very good - with a nice mix of pellets and whole foods that seems to make it easier to transition birds from a straight seed diet. Isis loves it *almost* as much as the Harrison's.
(http://www.24parrot.com/OptiBird-for-Medium-Parrots--4-sizes-P565002A/)
As to the other brands - personally, I've not found any of the other pellets to be very good (especially the 'coloured' ones like ZooPreem or Pretty Bird); they might be cheaper, but all those artificial colours and flavourings can't be good - and if they were really that good, why would they need all that extra stuff to tempt the bird to eat it?
Isis wasn't impressed with them either...
But please remember - even if you are feeding a purely pellet diet, you still want to make sure to provide lots of fresh veg and fruit too! Like captwest, we give Isis a veg-and-fruit meal first thing in the morning: normally made up of lots of green veg such as beans, peas, brocoli, kale, sprouts etc, together with Vit.A rich veg like carrots, peppers and chilies etc - mixed with a few chunks of fruit like melon, apple, pomegranate, grapes etc. She tucks into that whilst we all eat breakfast, and then if there's anything left after a couple of hours, it gets taken away and replaced with pellets for the rest of the day.
In the evening she then also gets a very small sample of whatever (parrot-safe) veggie food we have for supper as a small treat (she *loves* anything pasta based, but also goes bananas for a bit of baked potatoe





