I own the Sigma 105. I originally had it on my D90 before getting the D300s. I absolutely love it. Youll adore the extra reach the 105 gives you, even if it is extremely minimal. Everyday I wish I had the 150 or 180mm. The Tamron is renowned for being a wonderful lens, especially the 90mm. I, personally, think it is a tad short for animate critters such as bugs. It is known for being one of the sharpest macro lenses, however. Almost all macro lenses from all four major companies are sharp..its just the nature of macro lenses, but the Tamron 90 is known for being among the sharpest, as much as possible. Ive never had sharpness issues with my Sigma, however. I would save for the Sigma 150 or 180, personally. If you want something shorter, Id go for the sigma 105 because of the little bit of extra reach given. Its a wonderful lens.
True, but with the front element of the glass being so far into the actual lens, you never actually need to use the lens hood. I think Ive used it once. To see how it fit . As for getting close, all 1:1 macro lenses get you the same distance. Each one will get you to real-life magnification. Getting plenty close is actually the problem here. The Tamron 90 gives you a Minimum focusing distance of 11.4" (and both lenses take up 6" of that!). The Sigma gives you a MFD of 12.3". This is only an inch, but when youre working with critters less than that in total length, 1" is more than enough to make them flee. You want as much working distance as possible..
All joking aside, the Tamron really is a pretty lens. Ive never seen one in person, but the online photos really make it look pretty. I dont much care for the exterior on the Sigma. This, however, doesnt matter much after the photos are on the memory card, however.