I am someone who also likes both designs on her, and like Karnavaly said the redesign was kind of the anime's interpretation of X/Y's trainer customization feature.
When I first heard she was changing her look I was very sceptical as to how it would be handled but I was happy with the way it turned out, and like many it was odd to see such a change at first it had since grown on me fast because I feel like she can work many different hairstyles. The new design in particular had more appeal to me, especially because it seems to make her feel more like an individual, and the confidence boost she got from her makeover.
I also knew her short hair wouldn't suit her original outfit, because to make her resolve look "complete" she needed to have a new outfit as well, to signify a new reborn Serena, which really ties in with the fact that in the culture for a lot of Asian countries (such as Japan), a haircut is meant to signify a new beginning.
The hat and boots give Serena's new design a sense of maturity, but the ribbon will always be my fave part of the new outfit, because it always reminds her of Ash and his "never give up" remark. Now every time I think of Serena, I always associate the original design with her game appearance and the new one with the anime appearance.