Who will you actually be doing the CMAS training with? I.e. which national federation? The thing is: there's CMAS and then there's CMAS....
CMAS standards are one thing, however the actual implementation of these in the national federations is.....well...mostly abcent and at best very different from federation (country) to federation. Hence, a CMAS certificate in one country doesn't necessarilly correspond to the same CMAS certificate in another country. Interresting, no?
While I agree that many CMAS-affiliates do provide solid training, there're also some which do less so (I know countries where a CMAS * certificate can be taken exclusively in a pool, where the student doesn't learn tables or any theory nor does even learn to control his bouyancy independantly, but has the instructor do so during the dives).
Also notice, that a CMAS * diver isn't supposed to be "autonomous" -- i.e. is always expected to dive with a "higher ranked" diver and cannot just dive with another CMAS *. A PADI OW is supposed to be able to dive with another PADI OW certified diver.
CMAS and PADI are both recognized almost the same around the globe. No real differences there.
However the mantra around here seems to be that "it's the instructor, not the certificate, which a good diver makes". So if you find a good instructor who actually teaches you to *dive*, then the text written on the plastic-card isn't really important. How to find a good instructor, you ask? -- now there's another thread....