Don't get the klipsch speakers if you are interested in full frequency response in the low end. They sound great in the mid to high end, but with the klipsch 2.1, the sub sucks. It's nice and musical, but it does not go low at all.
I had a 2.1 and hated it. I got a klipsch 5.1, and it's a lot better - dual 8" sub vs a single 6.5" in the 2.1.
I still feel like the Logitech speakers have a much better low end response, but if you like the highs more than the lows get the ProMedia.
If you listen to hip hop, reggae, or other bass-heavy types of music, and especially if you are used to having a good sub in your car - like a quality 12" or something - then no doubt about it, get Logitechs.
Of course, you could always use a home theater receiver and buy component speakers
~MiSfit