They are great perennials that should be included in every sunny garden. And don't worry about how to pronounce peony. The herbaceous variety is divided into common and fern leaf types. It can be hard to decide which ones to grow, especially when you are trying to choose between all the shades of white, pink and red. They have beautiful, large flowers and are hardy through Zone 3.
Tree peonies seem to be a little more difficult to establish, but are well worth the effort.
The bloom season for peonies ranges over a period of 4-5 weeks. Early blooming varieties start in late May, mid-season varieties in early June and late season peonies bloom in the last part of June. Both are excellent and there isn't any gardening reason to choose one over the other. If you need a larger plant, you may want to start with a peony that is potted and actively growing. Bare root peonies are often the same size division, but they take a little longer to establish.