If you had to choose a single light shaping tool, you might do well to pick the silver Westcott 7' Parabolic Umbrella. First of all it's a really big, broad light source that wraps light around your subject yielding clean highlights and rich open shadows. But due to the special shape of the umbrella there's a unique mix of soft enveloping light with the kind of crisp detail you only get from reflectors. Put another way, if you combined a beauty dish with a softbox, you'd have a parabolic umbrella.