To be honest, i like all flowers! They all look nice and can all be used nice for decoration in your town, i think that using a bit of every kind of flower is the best way how you can decorate your town. It creates a lot of variety in your town and makes your town never get old in my opinion!
I like all of the flowers, having a special spot for hybrids since at the start I just had 1 or 2 pop up every few days and it would be a nice surprise. And later they were hard to breed, I always end up with white, red or black when I put together my pink tulips. Getting a purple one for the first time was out of nowhere. I tried breeding blue roses for at least half a year until I gave up and bought 2 from someone. And for a short time I switched the Beautiful Town Ordinance with another so I could make a few golden roses for decoration. Still missing purple pansies, but I'll try. They all look really pretty and I couldn't wait to have enough of certain kinds to arrange patterns and decorate my PWPs.
I do have a special little soft spot for blue violets and pink lilies.
Hmm... blue and purple roses I really love <3 I have a TON in my town surrounding my villagers usually <3 carnations are cute too! I really wish they had more or every colour at times :$