The Practice of Obedience

Christians have a complicated relationship with obedience. Those who strive to obey Jesus in everything at all times are often labeled "legalists." Others acts as if obedience is completely optional, since salvation is by grace through faith. Many are neither legalists nor antinomians, but simply pick and choose which commands of Scripture to obey. Who's right? What are we supposed to obey? And how can we do that?