The best sources are primary sources, or as close to primary as possible. Vital records from a town/county are good, as are parish records, generally speaking.
FamilySearch CAN have links to vital records and other quality sources, but those are the sources that should be added rather than a familysearch link to the person's profile there. The same is true of FindMyPast and I would think it would be similar for the other sites although I haven't used them.
When adding marriage records, it is important to be certain that the people named in the marriage record are the same as the children of the parents named in the profile; often people had very similar names, making it sometimes hard to discern.
Also, please be sure to retain the WikiTree headings and references tag (Biography, Sources, and the references tag immediately following Sources)