Which macro lens you get would probably depend on what kind of macro photography you want to do. There are a variety of macro subjects: flora, insects, still-life objects, abstract closeups.

If you wish to photograph insects, and are a beginner, a longer focal length that gives you more working room in front of the lens would probably be better. I am a Canon user, and I know that Canon offers a 180mm Macro lens that fits the bill. The greater distance between you and your subject reduces the chance you'll be scaring your subject off.

If you wish to photograph flora or still life objects, a 105mm Macro will do the job. I have the Canon 100mm Macro myself, and it is a great focal length. You have a lot of control over depth of field with this focal length. Its not too long, so you don't have to be over a foot away from your subject. If you need to get in really close, you can always get a set of extension tubes to reduce your distance to subject.

There are also macro lenses in the 50-60mm range. They tend to have a shallower depth of field, but let you get closer to your subjects. To me, DOF is one of the most important factors of a macro shot, and I like the extra DOF versatility a 100mm lens gives me.

So, to answer your question, the Nikon 105 Macro would probably be an ideal lens for most subjects, although if your subject of interest is the insect world, you might end up scaring off more of your subjects than you would wish (at least as a beginner.)