I can only say the 60mm Micro is one of the best bargains in the Nikon line. It's also fast and small enough that I carry it instead a typical normal lens. I've used (and fortunately can borrow) the 105 Micro. The 105's longer focal length is great, but it's more expensive an is quite a bit larger than the 60. Micro Nikkors are some of the best lenses ever made.
I'm not familiar with the operation of the Tamron, but the Nikons provide both a focus limit switch, and a manual focus switch on the lens. Both of these features are VERY good to have when you're working with macro. Without the focus limit, you can give your camera's focus motor a real workout going from infinity to macro. You'll appreciate being able to switch to manual focus easily when working up close... the camera will do a lot of hunting and you'll find autofocus gets in the way in a lot of situations.