President Obama's agenda the next four years could be a boon or a bust for some stock sectors. Here's an overview of what investing strategists say are the best sectors to buy and steer clear of. Health care: Among myriad changes, the sweeping ObamaCare plan enables more than 30 million uninsured Americans to receive health insurance. This brings an onslaught of new customers to hospitals, health insurers and drugmakers, but the added rules make