The SpaceX BFR will be completely reusable and will lift 100 tons of payload into space.
The NASA auditor has just produced a report which indicates the first test flight of the first version of the SLS will likely slip badly from June 2020. I think the first test flight slips to at least 2021 for sure and could easily go to 2022 or even 2023.
This will mean that at the end of the 2021 SLS contract, Boeing will have used up another $8.9 billion for a total of nearly $21 billion and will not have test flown for the first time. It will likely mean at that point in 2021, SpaceX would have a vastly superior SpaceX BFR having made multiple orbital test flights.