What makes a macro lense more detailed?

Looking for a macro lense for my Nikon D3000 - I'm new at photography with D-SLR cameras and I want something that can be zoomed in for very detailed close up pictures, so, for example, what is the difference between a 105mm and a 90mm macro lense? And what type of macro lense should I get for extremely close up photos?

The only difference between a macro lens and another prime with the same focal length is that the macro lens can focus closer.

A macro lens is optimized, i.e. Design to focus very closly.

A 105 mm lens has longer working distant than the 90 mm one (not much.) When compared to the 50 mm, when focused to 1:1 (life size), you have to be so many inches from the object. With the 105 mm lens, you have more room.

This also means the longer lens is more difficult to use, because you have to hold it very sill.

A real macro lens is optimized for close focus. It will be particularly better than a normal prime lens in terms of flatness of field, corner sharpness, and lack of pincushion or barrel distortion. No essential difference between a 90mm and a 105mm! Also there's no difference in the difficulty of holding the lens steady. That's a factor of the magnification, rather than the focal length. But you'll want to use a tripod or some other sort of device to hold the camera steady anyway, because depth of field at high magnifications is negligible and you'll want to stiop the lens down as much as is practical.