Are you asking about power conditioners/regenerators, or are you asking about balanced power units (like Equitech)?
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They are totally different devices. A regenerator (I recommend the Exactpower EP-15A) reconstitutes the wall AC to produce a perfect 60 cycle sine wave at a a constant 120 V. In addition, most also provide EMI, RFI and Digital noise filtering along with (some) surge protection. This is the unit you should buy first.
Balanced power (best for front end stuff not necessary for amps) splits the AC potential in two. Instead of 120V between the the hot blade (of the plug) and the (nominally zero) neutral blade (plus your ground of course) it splits it so that there is +60 V from one blade to ground, and -60V from the other blade to ground. You still get 120V between the two plug blades, but the blades are always opposite polarity relative to ground. So any noise carried in the line (mostly hum but also RFI) is self-cancelling. Studios have used balanced power for years, but it was only UL approved for consumer use about 8 years ago.
All that said, if you are in a position to install dedicated AC lines for your system, that will give you a lot more bang for the buck. All you need then is surge protection, which IMO is best done at the breaker box.
Dbld -- one way (to get protection at the breaker) is to wire a small high-speed diode from the "house" side of the breaker to ground inside the panel. If there's a surge, the diode will "ground" the breaker instantly tripping it before the surge can go down the line (the fried diode must be replaced but, they're only a few cents) This method does not comply with electrical codes in some areas but it is effective.
Another way is to install devices such as specialized breakers or surge devices mounted at the panel itself (cost a few hundred dollars) designed to protect the several circuits. These are "resettable" and for that reason may not always trip at a low enough threshold to protect delicate equipment.
I recall reading about some of this equipment on these forums, so you might try a search here.
One unit you want to take a closer look at, in addition to the ones you listed, is the Exact Power SP15A, alone or togehter with its balanced brother, the SP15 A. I had the same choice at my time (three or two years ago), and think the EP is superior to the Shunyata and PS Audio, esp. as far as practical considerations - e.g. plugging in power amps, space, and money-performance-ratio are concerned. Take a look at the archives here, and check out their site exactpower.com
I guess I didn't specify in my earlier post, but I use both Exactpower units, the EP-15A (regenerator) and the SP-15A (balanced power unit). Either one can be used alone, but the optimum setup is to use the EP to supply (unbalanced) power to the front end stuff (amps, powered speakers and/or subs) and also to power the SP unit (balanced power) which can then supply all the front end/source stuff. This is what Brent Jackson at Exactpower recommends and I have found it works beautifully.