All 1:1 macro lenses are sharp. All of them. So the deciding factor is working distance (related to the lens focal length) and other features of the lens.
Long lenses like the Sigma 150, Tamron 180 and Nikon 200 are great for insects because they have a long working distance so you don't scare the bugs away. However they are hard to hand hold and are fairly large and bulky. You really need a tripod for greate 1:1 shots with these lenses.
Intermediate lenses like the Nikon 105, Sigma 105, Tokina 100, Tamron 90 and such are good for a variety of purposes and are usually good for most insects and for most flowers. They are also easier to hand hold, but you get better results with a tripod.
Short focal length lenses like the Sigma 50, Nikon 55 f/3.5, Nikon 55 f/2.8, Tamron 60, Nikon 60 f/2.8 AF-D and Nikon 60 f/2.8 AFS, Sigma 70 and Nikon 85 are better for flowers, stamps and coins than for insects. They are easier to hand hold and are usually smaller and lighter than the longer lenses.
The ultra short macros like the Tokina 35 and Nikon 40 have a very short working distance and are best used to provide perspective distortion and other effects. They are almost useless for bugs and such. They are easy to hand hold, but since the front element is so close to the subject, you can sometimes get shadows or shading of the light on the subject from the lens shadow.
The Tamron 90 and the Tokina 100 are the most versatile budget champs, followed closely the Sigma 105. You can often find one new, refurbished or used for $400-450 or so.
You can find reviews of these lenses at photozone.de, lenstip.com, and slrgear.com. I have the Sigma 150 for bugs, an older ( 1983) MF version of the Tamron 90 for most everything else, and a really old (1966) Nikon 55 f/3.5 (AI'ed) that is great for closeup shots. I love them all.
I also use the Marumi 330 +3 closeu up lens (+3 diopter) on my Nikon 70-300 VR, and my Canon 500d closeup lens (+2 diopter) on my Nikon 55-200 VR since I usually take these lenses along when shooting wildlife, landcapes and everyday shooting. These closeup lenses allow me to get closeups (not 1:1 macro) when I am out shooting other things, and I can combine them with my macros to get greater than 1:1 if I want. These closeup lenses are a lightweight and inexpensive addition to the shooting bag. IQ is not quite up the the same level of the dedicated macros, but it is not bad if you get a premium closeup lens (the cheapy sets are not worth your money).
Good luck!
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Catallaxy
