It all depends on what suits your dog best - Pearl loved Applaws but it was too rich for her, She turned her nose up at Burns, likes Barking heads and loved being raw fed but it made her constipated (even without bones...). She's on Skinners salmon and rice and keeps a constant weight plus seems in good condition.
Has Millie recovered from her upset tum? I think I would keep her on the same food until she's completely back to normal before trying new brands/flavours......