I don't have the Nikon lens, but I do own and use the Sigma 150 (latest version with OS), an I also have the Canon 60mm macro and 100L macro lenses.

For handheld use, the shorter focal lengths are a bit easier to use and to hold steady (which is very important with macros). The OS or VR or whatever it is called by various manufacturers is almost useless for real macro shots, but is very usefull when you have some distance between you and the subject.

The longer the lens, the harder it is to keep it steady enough for good, close-up macro shots. On a tripod, it doesn't really matter.

As far as IQ goes, the Sigma is superior to my Canons, but the Sigma is big and fairly heavy too.