There have been a lot of discussions on SCUBA forums about this. Many of us here in the states would like to see an increase in teaching standards and qualification. It's been a while since I compared them but if I remember correctly, the CMAS1 standard is the equivalent of the our Basic Open Water + Advanced Open Water + Rescue diver certs. US dive industry doesnt want to change because they are afraid of scaring away potential new divers.
I refuse to enter in certification discussion, because for me everyone is making bubbles underwater
PADI has great advantages, the quality insurance is unbeatable...which is not the case of CMAS. PADI is very commercial, many modules, up sells BUT it's a good way to learn and discover scuba diving.
The PADI cert is very secured (too much maybe ?) and really fit to 95% of the market demand.
CMAS is based on the french way of scuba diving = professionals instructors with state diploma and high depth / high autonomy targets. Those particularities are related to the fact that below 100ft in France, you don't have some much to see compared to the Caribbean or Asia. A CMAS Level 2 is 130 FT depth cert and a CMAS 2* is 200ft with AIR mix (!).
I come from a CMAS certification path but did passed my PADI Divemaster and TDI Tech Dive cert to be able to dive worldwide whatever the needed certification. Whatever the certification & level you may have, when I arrive in a new club, I always like to have low depth <100ft dive with the local instructor to start to know each other.
PROs
CMAS => when autonomy, depth and experience is needed for diving "off roads"
PADI => same course worldwide, VERY secure, clear path, lot of specialties to discover
CONs
CMAS => the course quality relies 100% on the quality and skills of your instructor till Level 4 which is already the equivalent of a Divemaster ++++ level.
PADI => more expensive, VERY commercial, low autonomy (before the Divemaster), low depth!