Good question... and I would love to hear some other replies too!
Casey was weaned on to the Tropimix I believe but I see it more as a treat thing. We bought her the Hagen Tropican and Zupreem Fruit Blend when we first rescued her and mixed them together (way more Hagens and less Zupreem because I heard it had more sugar in it). At the beginning she would only eat the Hagen pellets then one day I noticed her picking out the red ones. Now it appears she likes the Zupreem better!

A couple of weeks ago she was on a "banana shape" binge and for the last couple weeks she had been eating mostly the red ones and some orange... now her poop is red!

It looks like in the evening she prefers the Hagens though... I really don't know how she decides to eat which one and when?!!?

Now I have been told by a local breeder/friend that the Zupreem is healthier and the Hagens goes bad really fast and isn't as good... hmmm.
I think for the sake of the coloured poo I would really like to switch her to the Zupreem Natural since it appears to be a good pellet and she likes the shape of them.
We also have the Hagen's Tropimix for Small Parrots and she gets it as treats. I believe that there are too many fatty/treat things in the mix to give as a staple diet. If I mixed it with her pellets she would only pick out the walnuts, peanuts, sunflower seeds etc. and not actually eat the pellets so she only gets that in controlled amounts in a separate dish from her pellets as treats when we go out or something.

I really don't know what pellet that is in the picture, it does look like Zupreem and something but I am not sure. Our Zupreem doesn't have pink, purple or blue pellets and the other whitish/brown pellets are a different shape than I have seen too?

If you do switch you have to monitor his weight etc. I have tried taking the Zupreem out slowly to convert to Hagens but she'll go on strike until the Zupreem comes back... even though she likes the Hagen's too!
Oh well, maybe we'll by a bag of Zupreem Natural and see... I really wish they would give out samples!

Good luck!