I use Sigma 180mm and 105mm macros on a D70. Both are exceptional lenses which are sturdy enough to withstand regular use in the field for herp photograpy. The 180mm is very useful in photographing skittish subjects because of the long working distance. I've never used the Sigma 150mm but have heard it, like the 105mm and 180mm, is an optically excellent lens. It has a slightly shorter working distance than the 180mm, but is lighter and therefore easier to handle.

Here are a couple shots taken with the 180mm on a D70. Both photos are uncropped.