Family Search search engine
I consistently find that I can find records easier in ancestry.com as compared to familysearch. A typical example which has happened many times (50-100), is that I first search the familysearch records and find nothing useful or nothing that is clearly my ancestor's records. Then I go to ancestry and find something. I again search in familysearch as I would rather attach records directly from family search since the information gets automatically put into my ancestor's record. I can't find it. Then I attach the record from ancestry and once the page refreshes, familysearch now gives me that same source as a suggestion.
There is something deficient, it seems to me, about the familysearch search engine (or put another way, familysearch should figure out how ancestry does it). For example, I have found a source in the 1939 England and Wales Register in ancestry. I actually go to search Collections in familysearch and search on the 1939 Register and nothing comes up, but then once I put in the new information and refresh, there it is in familysearch.
I also find that if I am searching for sources for a woman in familysearch, even if her husband is in the system and linked to her, it can virtually never find a record using her married name. Even if I add an alternate surname, that rarely helps, whereas, ancestry consistently does make that connection of linking the woman's given name with her married surname.