I think the AMA is doing the best job right now simply because they are the largest. They are intimately involved with health policy right now, and were recently rated as the third strongest lobbying organization in Washington. People on both sides of congress listen to AMA's viewpoint because they represent the largest number of physicians. AMA is a huge organization that has its hands firmly around very different issues: they are leaders in advancing science and medicine with JAMA, they are the leading political lobbying group for physicians, they are one of the biggest advocates for public health issues, they are ultimately in charge of health education being connected with national groups like AAMC, NBME, and ACGME, they are leaders in implementing EMR and P4P nationally, they are the sponsoring organzation for the largest medical student group in the country with the AMA-MSS. I could go on and add a few more, but I think you get the point. They are fighting for physicians, but they do so in many ways other than just politically.
As for the falling wages, the AMA has definitely been leading the push in DC to get the SGR fixed so medicare reimburesments stop falling. They've successfully prevented cuts the last several years and are now working on a permanent fix.
I think your comment about universal healthcare is stated incorrectly. You automatically assume that universal healthcare is detrimental to physicians. I would respond by saying that some universal healthcare proposals are very detrimental to the medical profession, but there are other universal healthcare proposals that are very beneficial to physicians. For example, at least 10-20% of care given by most physicians will be uncompensated. With universal coverage that 10-20% uncompensated care will be eliminated, and assuming that reimbursement levels stay the same for procedures then doctors stand to increase their salaries fairly significantly. Many people (incorrectly) assume universal healthcare necessitates government sponsorship control. All universal healthcare means is that everyone is given the opportunity to have health insurance if they want it. There are a multitude of proposals out there (including one that the AMA has written) that will cover 100% of Americans without turning us into the Canadian system.
In the long run what is good for patients will be good for physicians and what is good for physicians will be good for patients. That may not be evident if you're taking a short-term view, but given time it will become evident.