If you are doing extreme macro work, focus-stacking, and using lights, the MP-E is the way to go. It's an extremely specialized lens and thus takes a LOT of effort to get useable results from.
If you want to dabble in macro, shoot some bugs, flowers, and then shoot some portraits or landscapes (or anything else not 30cm away from your camera), the 100mm (non-L) is the best bang for your buck. Assuming you have a kit lens (18-55mm or so) then the 100mm macro gives you a relatively fast (f/2.
, USM-focusing, longer-ish telephoto lens. Skip the 60mm tbh, the focal length is likely too close to what you already have, and the price differential isn't *that* large. Plus the 100mm is future-proof in that it's EF and not EF-S in case you ever move up to full-frame or a film SLR. I'd also say that if you're on a budget, the non-L version (which I've had for years) is just as amazing and shares filter size with a number of great, cheap lenses from Canon as well.
Forgot to mention - if you want higher magnifications from the 100mm just buy a few extension tubes (not extenders) and you'll get higher magnifications when you want and need them, and then be able to go back to using your lens as an all-purpose lens again after.
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