Which one is Sigma's best current Macro lens?
If you had to pick one of these lenses - which one would it be and why?
I added my personal comments for each of these lenses, feel free to add yours ...
50mm EX f2.8: small and lightweight, quite sharp, - very short working distance (sold it for that reason)
70mm EX f2.8: relatively small and lightweight, quite sharp, - still relatively short working distance, but serves as a nice medium tele-lens as well
105mm EX OS f2.8: size wise a slightly bigger lens, but does not extend (IF), build-wise it's a huge step up from the previous version; sharp
150mm EX OS f2.8: bigger lens, quite heavy, you need a tripod (why OS then if it makes the lens so much heavier that you most likely need a tripod?), sharp. I find this lens quite difficult to handheld, even with OS on - it took me some time to get used to shooting it. The previous version of this lens was considerably lighter and hence easier for hand-held shots.
180mm EX OS f2.8: can't comment on this one as I never had a chance to shoot it. But I had once the 180mm f3.5 lens which was quite nice but very heavy.
To me it's a difficult choice: Maybe the 105mm lens I would keep out of all of them - it's not too big and not too small and offers a good working distance. I do quite like the 150mm as well and the 70mm, but last one more as a medium-tele lens.