Yup Uni was like this exactly when she was still adjusting. She'd eat one food, then decide she didn't want it anymore after a few months, and it always seemed like it was just after we bought a new bag. I think we tried about 3 or 4 different brands before she finally settled on one.
But of course they will like the kibbles and bits better, it's like feeding kids Mcdonalds or a grilled chicken salad, of course they will prefer the McD's
but you can't have that everyday.