I've got a Minolta 50mm/2.8 macro lens and I must say it impressed me in every respect so far. The sharpness of this lens is probably in the minolta elite league being even noticably sharper at 2.8 than 50/1.7 at the same aperture. I also found autofocus pretty good unlike many other people who say they have to use manual focus most of the time. The thing is that if you switch the AF mode from wide to local in the menu, you can autofocus pretty much on anything you want (at least from my experience). See for example this shot of a water droplet on the leaf:
The good news is that I usually get pretty crisp and sharp pictures handheld most of the time (but with ISO 400-800) and am happy with 70% of shots. So yes, this is a very good lens to get if you come it by on ebay or elsewhere (I bought mine locally).
For the insect you probably will need 100mm working range but as I understand it will also be more prone to camera shake and a tripod becomes a necessity. That being said, I've recently been lucky to shot reasonably good macros of bugs:)
I cannot comment on the performance of other macro lenses because Minolta 50mm/2.8 is the only one I've used so far.