What's the best way to cook fall-off-the-bone baby-back ribs
I rarely ever recommend boiling the heck out of meat.  You are washing away all of the flavor.  Remember water is a solvent and remove everything from the meat if it is left to boil long enough.  For the most tender ribs I would recommend a braise.  The slow, low, moist cooking of a braise is perfect for breaking down connective tissue in the ribs without drying them out or washing away natural flavor.  Even in smokers I haven't had great luck with baby back ribs as they have a tendency to dry out.  

Here is a easy to follow braise for ribs by Alton Brown video, 1, 2.  It's a decent place to start and work on your preferred methods from there.  

Please avoid boiling your meats, you will be so happy with other methods, even if they do take a bit longer.