Check out http://www.google.com/search?q=bankruptcy+preferential+payments
and check with your lawyer to see how this may affect your case.
Bankruptcy entitles you to walk away from most debt at the cost of having the bankruptcy on your record for ten years. I would recommend not reaffirming only certain debts because other creditors may ask why you can afford to reaffirm some debts but not others. If you want to repay every creditor, look at getting a Chapter 13 rather than a Chapter 7 bankruptcy.
The doctor business is just that, a business, and they will write off any losses they incur. Its nothing personal, unless you have a very unusual case. Your provider may be very understanding and continue to provide services to you regardless of whether the cancelled dept is reaffirmed or payed back.
Bankruptcy courts don't like favoritism and neither will the creditors with whom you don't reaffirm your debts if they decide to inquire. Certain creditors are more vocal than others when it comes to bankruptcy, so they may or may not follow up.