They'll probably resemble the gold cap the most, although technically speaking, you can have 3 offspring who each appear differently... one who appears most like the father, one who looks most like the mother, and one who's somewhere inbetween. I will say though that green is dominant over yellow and orange colors, therefore, you'll end up with chicks who look most like gold caps however may have some features of a sun conure...
For example, here is a mitred x sun conure hybrid. It has most of the features of a mitred conure due to the green dominant color... However, that red on the stomach is dominant over green. These are just baby pics, so he's been coloring up some yellow in his face, too! As he gets older he ought to color up with some more red on his head and who knows how much yellow.

And the next is believed to be a hahns macaw hybrid (I can get pics of another one that the hybrid species known for sure) x sun conure (but could be a jenday). You can see the hahns in the facial area, and the sun in the coloration on the head. There's a little bit of red in the stomach, but otherwise it's a predominantly green bird.
