In general, my approach is to shoot in Av with the widest aperture that gives me enough depth of field, and at the lowest ISO that gives me a fast-enough shutter speed to achieve no-shake or desired effect, regardless of light levels. If I have consistent-enough subject locations and safe light locations, I'll use 1-3 remote flashes on stands triggered by PocketWizards. If I don't have good conditions for remote flashes but I do have a good-enough ceiling, I'll use bounce flash. If I can't use bounce flash, I'll often go without flash. I have a pair of Sto-Fen diffusers but they rarely get used. More often I'll just use a small cut of Rosco 103 as a start, and an umbrella if I need more effect.