Cubase is obviously the best because that's what I use.
Sonny is right, though: they're all good. Most of the opinions people have about the differences in the programs are really about the interface and not the quality or performance.
Since you'll get good at using whatever interface you end up with, take a good close look at the specs, try the demos, and go with whichever one suits your fancy.
Here's my impressions- which are sure to be at least a little wrong:
Sonar: Probably the most MIDI oriented, though still handles audio just fine. Probably the most popular, too, as people start with cheaper cakewalk products and stay with the familiar interface.
Cubase: Jack of all trades, master of none. Does it all (to a point) but doesn't really shine in any one area. Potentially has the best VST plug and synth integration, but probably only slightly so. (Steinberg created the VST standard.)
Logic: Seems like the most uptown of them all- you can go all the way to dedicated hardware interfaces with it if you want. Most home users never will. I've heard that it is a complex program but quite powerful once you get it down.
Have fun exploring,
Chris