While the CWNA provides the technical know-how to be a WLAN Admin, it essentially stops there. You are taught meterial regarding antenna placement/mounting, RF math and system operating margin, type of losses and attenuation, etc etc etc, not much of which will help you outside of that direct speciality. Course guide HERE.
With the ECSA you are gaining a much wider range of skills, including the information the CWNA course would have you learn, which will drastically change the way potential employers and coworkers will look at you. Without writing a seventeen page essay on the matter, the course material can be found HERE. What you can tell while scanning through it is that the amount of material being thrown at you is pretty intense. Not only will you have the technical knowledge regarding the systems you are working with, which is necessary when performing a security assesment, you will know how to respond to a wide veriety of situations in a manner than enhances the overall outcome of the tests rather than hindering them.
That being said, they are both 5 day courses. The CWNA is a foundation level cert for their higher level CWNP, which reportedly make an average of 105k/yr. The ECSA, however, is a step below the Licensed Penetration Tester Program which is very widely recognized in the industry as being among the best. I don't have figures for you but I'd all but guarantee that they are higher than the CWNA certified professionals.
Final vote: ECSA for me. After that's been tackled, LPT here I come....