Hi Brett,
Well it depends what you are after. The emitter/ softbox combo is for sure the most versatile method. You can quickly change the look of your highlights by moving your emitter or setting your planes translucency to your needs. You'd need a whole lot of different MXI's or HDR's to be that versatile. You also have the benefit of knowing that you did it the correct way- just to soothe your mind a bit when your regard the rendertims.

I cannot recommend this method for anyone not having a renderfarm at hand so mapped emitters with a high quality MXI will do the trick in most cases.
I use all the methods you described above from time to time, I use bouncecards rather seldom sometimes a directional grid covering my emitters ( for example in my closup of the faucet in the countryhouse to really punch out the metall features without lighting the rest of the scene) and SSS diffusor planes when I'm crazy and have plenty of time.
regards,
Ben