It depends on what type of Macro shots.
. If they are static or reproduction, as in stamps or coins or small flowers, then the 60mm is the best. It is the most linear of all the macros and has the least CA
. For bugs and other skittish creatures, where you need to keep a distance between the lense and the bug, longer focal lengths (which have longer working distance) are better. The 180mm or 200mm are best, but more expensive. The 105mm and 90mm are most used as they are less expensive than the longer focal length lenses and are good enough for most jobs.
One accessory you must get if you are serious about macro photography is the close up flash.Most of the times the built in flash is just not sufficient - in power or reach
If the body has no commander mode then
R1C1 Wireless Close-Up Speedlight System from Nikon
If it has then
R1 Wireless Close-Up Speedlight System from Nikon
The difference is that the former has a wireless command attachment for the bodies that have no command mode - D3xxx and D5xxx series.
Normally unless you are a professional macro photographer, just one macro lense is sufficient, but there is no harm in having two if you can afford them
. 60mm for reproduction
. 180/200mm for field work
I would stay away from DX macro lenses, as a macro lense last practically a life time (unless some new technology comes up), so limiting one self to DX does not make sense.