The MP-E 65mm is not a normal macro lens, it's a special lens for extreme macro only.

If you need 5x magnification the MP-E 65mm is the only option on the market - so it's obviously better than the other options (well, you can potentially get 5x with extension rings or reversed lenses but the MP-E is the only lens that is designed to work at those extreme circumstances).

However, if you want a lens that can also be used as a general purpose lens the MP-E is useless - it only does macro.

The MP-E 65mm is designed for one specific task only (macro at extreme magnification), if that's what you want to do than it's absolutely the best option, but it's completely useless for everything else.

By the way, if you want to shoot handheld macro than the Canon 100mm f/2.8L has a new image stabilization system that works for macro, and I believe that right now this is the only lens in existence that has that system, it's also the only lens out of the 3 you mentioned that has auto-focus (and the 100mm, unlike the MP-E, can also double as a great portrait or general purpose lens).

The Zeis is probably great optically but it doesn't have auto-focus or IS like the Canon 100mm (that's not a big deal for macro but does limit it's usability for other situations) and it doesn't have the extreme magnification of the MP-E.

So, there isn't really such a thing as "better", each of the lenses you mentioned is significantly better than the others at some aspects and worse at others.