Elixir features meta-programming, structs and protocols, first-class documentation, strong focus on the tooling, some abstractions that make concurrency more accessible (such as tasks and streams), etc.
However, Erlang and Elixir share a lot! They have the same data-types (with the same names and even the same syntax for almost all of them), the runtime is the same, and the same foundation about processes, fault-tolerance and distribution.
My suggestion is to go with whatever "touches your heart" because, even if Elixir has its own features, they are more alike than they are different and most concepts you learn for one will also apply to the other.
