If your shooting wildlife, bugs etc then I'd suggest a minimum 100mm lens, the working distance is a tad larger and its easier to frame up shots without scaring the insects away.
If you can afford it the canon 180mm or sigma 150mm would be great for wildlife as the working distance will be even better but they are heavy lens.
If your doing still life then a 50-60mm lens will be fine and also doubles up as a good portrait lens.
forget about the MP-e its a specilist lens and require a lot of technique and light to get the best from it.
all dedicated macro lens will produce 1:1. If you want higher magnification then extension tubes are the way to go, but this will likely also require a flash unit of some sort as the light drop off it substancial.
Forget about IS and auto focus if your shooting wildlife at 1:1. 99% of the shots will be manual focus and 100% if you're using extension tubes.
It all really depends on what you're taking pictures of. but a good starting ground would be a 100mm, whether its a camon, sigma, tamron, tokina, there all much of muchness. if you can afford it get the canon, if not any of the other 3 get good reviews.
I use the tokina with tubes and a homemade flash light rig. once you have the gear its all down to technique
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