Petunias are definitely my favorite annual. They are found practically anyplace that sells annuals, they are inexpensive, they have a wonderful scent, and you cannot beat them in regards to pure bloom power. These things bloom nonstop with large delicate flowers in an array of bright colors from May till your first frost.
Petunias sometimes have a reputation for being troublesome though, and I really do not think that is fair. The problem is that most people tend to plant annuals in pots. Don't ask me why, but it seems people think the ground is for perennials and pots are for annuals. You severely limit yourself when you do this though and you severely limit your plant possibilities.
The issue at hand is that petunias are not what anyone would consider drought hardy. To grow and to bloom then need water. So if you plant a petunia in a pot, especially in a porous one like terra cotta, it is going to dry out quickly and need watering every day or twice a day. Even then because of the limited space within the pot it will never grow that large. A store bought petunia 6 pack might double in size when planted in a 12 inch terra cotta pot, but it isn't going to get much larger than that.
Consider though, planting petunias either in very large pots or directly in the ground (or in a raised bed). When planted in this way petunias only need supplemental watering in the worst dry spells. Additionally they will have all the nutrients & moisture they need to really put on a show for you. A petunia planted in the ground can grow to more than a foot high and more than two feet across and be covered with blooms.
Plant your petunias in full sun for the most blooms, and also dead head, that is remove spent flower blossoms, when the flowers fade to encourage more blooms.
Petunias come in every shade of the rainbow except Orange, though I have seen some orangish ones in seed catalogues. When starting them from seed you'll want to keep them well watered and if you want them blooming in May you'll probably want to start them in early March. I have started them from seed before (mostly because I wanted to try some cool colors you can only get from seed catalogues) but it was a hassle. So in the future I'll content myself with the supply at my local home and garden store.
So if you have a bed that you really want to pop with color in the summer, plant a tray of varied colored petunias, you'll love the results. I have such a bed near the road and it is always turning heads.