Where you should search depends upon your topic. 
You'll be most successful if you search in a subject database that covers your topic.
For example, with a topic of the ethics of euthanasia, either Philosopher's Index or HealthSource would be excellent choices, depending upon what you'd like to emphasize.
HealthSource will emphasize the medical point of view, Philosopher's Index the philosophical point of view.
Interested in the ethics of outsourcing? Best bets: Business Source Complete or Philosopher's Index. The ethics of genetic engineering? PubMed or Philosopher's Index.
Image Source: Grafikę Stworzył. Compass. CC BY-SA 3.0. Wikimedia Commons.
