I use Camtasia on the Mac. The Windows version is also pretty good but very different in its feature set.
The most important feature for me is to easily do time remappings.
Not sure how this works in the Win version, but in the Mac version, I can just enable time stretch for a clip and then move the in- and out-point of a clip. The speed then automatically adjusts to fit the new length. Very valuable when I performed the action slower than I recorded the voice over.