Used to feed Zupreem but was never fond of the dyes and sugar in the pellets. In my conure, the Zupreem Fruitblend caused his droppings to be various colors and unformed. Other people have also reported this as well, but it's not something that occurs in all birds.
I feed both Zupreem Naturals (I personally avoid colored pellets) and Harrisons. My GCC only gets Zupreem (he doesn't care for anything else) but my Goffins gets both, plus Lafeber's Pellet-Berries.
Pretty much Harrisons, Zupreem, Roudybush & TOP's are going to be highly recommended.
Keep in mind, you might want your bird on a particular pellet, but your bird may not like that one. As MonicaMc said, try as many as you can to see what they like. You can often get samples so you don't have to buy a huge bag only to discover they hate it.