They are both good,
though the signal to noise ratio of the Logitech = 96 db is actually better than the Creatives = 80 db (decibel) so the sound will be clearer on the Logitech it seems (higher means better). As for the bass response, 40 is okay for a system like that (mine achieves 45).
The other difference is that the Creative has a lower wattage on the sub = 17W compared to 20 on the Logitech so that should be more powerful all in all.
But I'd say they are both about equal to the ear. I guess it all depends on the looks now.
They should both be about the same price too, though I'd go for the Logitech if it's not much more
Plus the Logitech has a seperate headphone jack on the unit so you don't have to unplug the whole speaker system from the computer if you wanted to have it quiet