Hello Jim, I have hired lawyers to handle my application for my wife and I, we have had a good experience so far and they have helped us a lot. By the way I am in Canada, and I think the immigration process is similar in many ways. (correct me if I am wrong)
when looking for lawyers, try to find an Immigration lawyers that has a lot of experience working with immigration. They will have more knowledge about immigration and the in's and out's of it. Do not pick a lawyer that has dealt with immigration only a few times, or has no experience with immigration. Try and find a reputable immigration lawyer.
You should know that hiring a lawyer will not make the immigration process go any faster (in most cases) and it will not guarantee your lady a visa to enter the United States. This is obviously immigration that decides when and if she will be allowed to enter your country. What the lawyers will do is make sure everything is completed and filed correctly before sending anything to immigration, this could be very helpful because if you make any mistakes on your application, or missing information or documents, then this will cause immigration to send back your application to you for proper completion, so in that respect hiring lawyers will save you time and headaches caused by any possible mistakes or missing information in your application.
good luck,