If I absolutely must narrow it down, Phormium tenax 'Bronze' is my go-to plant. If my gardens were a classroom and I the teacher, Phormium tenax 'Bronze' would be the teacher's pet. I am always looking for plants with stature, drama and the ability to be both a specimen and a part of the structural backbone of a garden. This big boy fits the bill beautifully. This phormium can grow to eight feet tall under the proper conditions, and it has the posture of a ballet dancer, with upright sword-shaped leaves presented with grace and precision. The dusky brownish red color is moody but not somber; it isn't so dark that it sucks in the light. Planted with the right companions, it can be the commanding anchor for a spectacular garden riot, or it can hold the center of a formal design with elegance (and a bit of swagger).
My favorite companions for Phormium tenax 'Bronze' (oh how it hurts to have to choose!) are:
Euphorbia wulfenii—its blue-green foliage provides a constant color contrast, and the bronze leaves of the phormium make a perfect backdrop for the euphorbia's conical (and comical) spring blooms.
Grevillea 'Robyn Gordon'—with this plant, Phormium tenax 'Bronze' has met its ideal match. The four-foot-high shrub cuddles up perfectly around the bottom of the phormium, giving it support and grounding it. In turn, the phormium's rich color and textural simplicity helps to give the deeply incised, fresh green leaves of the grevillea the appearance of being outlined. The unusual, shrimp-like flowers are a bonus, and they, too, are somehow magnified in the presence of the large dark phormium.
Pelargonium 'Chocolate Mint'—the perfect plant to this finish off this little mise en scene. The deep green, furry leaves have a maroon splotch in the center; the color connects perfectly to the color of the phormium. It is like a little Christmas tree skirt for the phormium—but with style.