FamilySearch is excellent and has a ton of primary sources once you get used to how to find them. Ancestry.com's main advantage is that it provides "hints" that suggests sources for your ancestors. It's super easy to add those sources and people to your tree. That's also its main weaknesses, because these sources and hints are sometimes completely wrong, and are then copied and repeated by many genealogists until they take on a veneer of truth through sheer repetition.