If you've got a Mac, Final Cut Studio is the best. It not only has FCP for editing, but Soundtrack Pro for sound mixing, Color for color correction, Compressor for converting to just about any format imaginable, Motion for 3D graphics and more, all integrated to work together.
For instance, you can send a clip with bad audio from FCP to Soundtrack Pro, tweak the sound to your liking, save it and the audio is automatically updated in FCP. You can roundtrip like this between all the FCS applications
Avid and Premiere are also very popular editing suites, and all three do some things a little differently. But they are all powerful and are more or less capable of doing the same things. Avid's been around longest so it is more popular, but FCP is eating away at more and more of the market every year, and the rumored upcoming refresh is supposed to be a big leap over the last few versions.