The 105mm Nikon Micro is very well respected partly earned during the 35mm film days. It's a great lens and would be the lens of choice if you can afford it. Seen 'em used in many professional science labs etc from years back using it as a 105mm on a 35mm camera. The DX format cameras mean of course you can use a shorter focal length lens to get effectively a similar focal length and I know many labs etc. now using the 60mm Micro Nikon as well. I have this latter lens and have no complaints or issues at all. I don't use it for close ups of insects or things that move etc. I tend to use it for photographing generally larger objects as I know it is well corrected at short distances unlike a 50mm nifty fifty. I have used it for close ups on small objects, bullets/cartridges, watch faces, medical photography, serial numbers. It too is a nice, sharp lens. Guess it depends on what you actually want to photograph. Have no experience of otehr brands.

Thanks for all of your comments. I've ordered the Sigma 105mm Macro and extension tubes. That should see me right for a while.

Nice - look forward to seeing the shots!