Hi Riad
The Sigma macro is the only non-Nikon that I use in my DSLR system, same when I was shooting Canon.
Actually preferred the 180 over the Canon 180 !! The only downside to the lens is when you sell it, will take a much bigger hit.
Presently I'm in the market for a Nikon Macro to use with the D800e and not sure what to do, will most likely go with Nikon. I like having some space between lens and subject so tend longer focal length. Looking at the 200 macro, which btw is one of the oldest if not the oldest design in their lineup.
Excellent advise from William and fully agree !!
al