Do you have friends who you can play R6 Siege with? It's definitely a better experience with a proper team that you can coordinate with. Also, I don't think there are local servers so that is also a factor to consider.
Ass Creed because Im a big fan of open world ninja games with vast city scapes and running on rooftops at great hights. Also, the Ass creed games have awesome stories.
Played siege, was alot of fun, assasins creed is the same as all the other hundred that have been released before this one, so I would recommend siege since it's something a bit different for a change.