After looking into the matter lately (cause I eat ALOT of salmon), I found that you are better off with wild salmon (Canadian wild is what I eat), however, eating farm raised salmon instead of wild is, although likely not quite as good for you, still a better choice than most foods. Farm raised salmon is NOT devoid of omega 3's or other beneficial EFAs (although the way the press makes it sound the stuff will kill you with just one bite).
If you default to the wild salmon choice, and eat farm when wild is just not available (or affordable), you will be just fine. In order to aquire a significant dose of the nasty stuff in wild salmon you'd have to eat a truckload. Just eat it, your still better off.
If I were you I'd be more likely to boycott wild because of the increadibly brutal impact it has on the environment rather than what it contains (or doesn't). Farmed salmon is KILLLING, yes KILLING wild salmon stocks in Europe (close to dead now in some areas), British Columbia, and now South America. Truly an evil industry.