Diffusers, as a rule, are all over the place in terms of efficiency. Higher-cost diffusers,. and larger-area diffusers, *tend* to be more efficient. In addition, high-pressure diffusers also tend to be more efficient.
However, the high-pressure diffusers can also be problematic, as the cheapo regulators (certain Aquatek models, as an example) have preset working pressures. Paired with the wide cracking pressure range of the Atomic-style diffusers, your rig may or may not work ...at all.
Unfortunately Evilbay links are automatically removed by forum software, so I don't have any idea what you settled on. Just read a bunch in the equipment forum, including the stickies, and I doubt you could possibly have any questions that have not been discussed in at least a dozen ways.
Any decent rig has a regulator with variable working pressure, a solenoid valve, and a needle valve, with a check valve along the line somewhere. Each of these components can be bought incredibly cheaply, though the less money spent is roughly inversely proportional to the rate of failure.