Either should work, but I would turn the bass down on the "subwoofer."
If a lot of bass is important to you, consider adding an actual subwoofer. What is called a subwoofer in small 2.1 & 5.1 speaker systems is usually just a separate woofer, a practice made popular by the Bose Acoustimass speaker systems. A true subwoofer is designed reproduce frequencies below 80 - 100 Hz, which is non-localizable by most humans (i.e., we can't locate the source of such low frequencies using our ears alone). Crossovers are used to ensure that the subwoofer doesn't receive signals for higher frequencies and the rest of the system doesn't receive signals below 80 - 100 Hz. This relieves the "subwoofer" of sub/satellite systems of the need to produce the most difficult frequencies.
Logitech's
30 Watts RMS rating should be taken with a grain of salt, since it is at 10% total harmonic distortion, which is a lot. That doesn't make the speakers bad; it just doesn't speak well for Logitech's marketing department. At lower power, the THD should be greatly reduced.
