Man this was extremly hard, my brain is still sore from chosing!! XD:
Bloom : both suit her so well, i didnt like her winx or charmix much at all so for me its the Believix outfit and the enchantix hair =P
Stella : i adore her skirt ♥w♥ and i am so glad they didnt change her hair in those two forms, it suits her so much, makes her less bratty. Enchantix just did it for me, her Believix is too casual, cute! but that top just doesnt cut it for me.
Layla : aww her Believix top is adorable ♥ but again, far too casual. Enchantix but her believix wings are perfect!
Flora : Believix, nevermind enchantix anymore. it was always cute but never amazing on Flora. Her Believix suits her so darn well!! it brings out her inner flower ♥ plus her wings are magnificent
Musa : Believix!!!! i wont look back on that choice, i loved her Enchantix but the believix is absolutly perfect for her. i think the colour choice was better too. the yellow on her enchantix was a complete mistake.
Tecna : were do i start?? they never make a mistake with Tecna, cute in season1, adorable season2, breathtaking season 3 and well yeah you get the picture!!! she never fails on cuteness. but because of her hair cut and the way it brings out her big eyes, Believix.