Perennial. Plant once & enjoy for several years.
Perennials have the advantage of living from year to year. In  most cases they bloom for 2-4 weeks. Some of them will bloom all summer. Annuals on the other hand will bloom all summer: Bloom, Bloom, Bloom! But life is full of trade-offs. Annuals have to be replanted every year. Choosing a range of bloom times for your perennials will give you some color throughout the summer. Choosing a condensed time-frame will result in lots of color during those times.

Most folks will end up planting a combination of annuals and perennials and shrubs. The shrubs provide the backbone of the garden (Ironically as I write that I lay in bed recovering from backbone surgery.) Perennials offer a huge range of shapes, and forms, and features. Both the shrubs and perennials will return year after year to your garden. Add in a few, or a lot of, annuals and you increase the amount of blooms substantially.