mwelsh, don't be swayed by people who push what they have.
And don't go crazy chasing the best setup possible. All of the major manufacturers' macro lenses are better than good enough. Better than good enough means exactly what it says. Buying any of them would not be a bad mistake. That said, if you were invested in Nikon I'd advise against the 200/4 MicroNikkor AI/AIS. It is useful but but not that good a lens; the newer 200/4 AF is much much better.
Buy the books I recommended, read them, then decide how much working distance you want. That's the big advantage of 100 mm +/- lenses over 50 mm +/-. But I had a 55/3.5 MicroNikkor for some years before the 100/4 MicroNikkor was introduced and didn't feel deprived when all I had was the 55.