If I listed all of my favorites, it probably wouldn't help you much.
But let's see:
I am always reaching for either Fishtail Flags or Fishtail Flags Layers, either for a sentiment or for an accent.
I love many of the MFT flowers: the Poinsettia is gorgeous
for the holidays. I use it a lot, but I'm partial to Christmas projects. I think my next favorite are the Hybrid Heirloom Roses. And then in no order, the Sunflower, Winter Rose, Hibiscus & Plentiful Petals. But the Flower Medley is great for lots of different petal shapes in one die set.
I love the Modern Morocco background die and the Chevron cover-up die.
Any of the pierced shapes (circle, square, etc.) add a nice little something.
Mona's Tropical Sensations stamps & dies are gorgeous flowers!
I love the Dainty Bows dies too for a cute accent.
And any of the Blueprints die sets are a great way to get a number of dies that all work well together.