Rosalina comes across as a Mary Sue. "Oh but she is so wise and motherly and has super cosmic powers!" At least she had an interesting backstory which showed some character, too bad that whenever she physically appears in the series it is as the most stoic Mario character ever and nothing like the storybook.
Peach has a lot more going for her in that respect. She's had a ton of history with the series which has developed her as a naive airhead always stumbling into trouble to the detriment of those around her. The RPGs in particular make her a very fun character to have around. As far as Daisy is concerned, being a hotheaded tomboy is at least something that sets her apart from the other two.