Smart does not always mean it will be obedient. Smart dogs tend to get into more trouble because they get bored easily. There are often a bit harder to train because they get bored with training. You need to find a dog that will thrive with your lifestyle. There are plenty of tests on the net to find the right breed for you, but in all honesty, any rescue will probably be just as smart as any breed you look for.
Depends on where you live. The most intelligent dog of them all is the Border Collie, though if you were to have one you would need a large back yard and a lot of time in the day to play with the dog and get him excercise. If you don't have enough time in the day to get a Border Collie then another very intelligent dog but more versatile is the German Shepard.
Any dog is trainable. You will NOT find one that is fresh out of the box obedient. You actually have to do some work and train it. Yes, some dogs are smarter than others... but they can all be trained to do what you want them to do.