When I shop for everyday flowers, the two biggest deciding factors in my purchase are form and hue — aside from, of course, vitality. For instance, I love the way the color persimmon looks against my peacock-blue walls. I also prefer a few blooms mostly for their shape, including calla lilies, peonies, and tulips. But if I'm hosting a dinner party and need those blossoms for a centerpiece, scent is the most important thing to consider.
For some reason, I think people tend to forget that flowers smell! I can't tell you how many luncheons and parties I've attended where the scent of the centerpiece has been so strong, it has either tainted the taste of my meal or made me nauseous. So in that case it's best to choose flowers that are mildly scented, such as ranunculus, yellow lilies, and hydrangeas. Steer clear of petals like sweet peas, most roses, and gardenias, and just use your judgment!