I have accounts both places and find way more junk on Geni than on Wikitree. Geni doesn’t have the emphasis on sourcing and bios that Wikitree has and they encourage downloading junk from MyHeritage and other sites. I have not found it particularly useful (I was asked to join to help with cleanup in a specific area). On the other hand, however, they have lots of members in other countries, so if your ancestors haven’t been living in the U.S. or the U.K. for the past two or three hundred years you may well find what you need there.