2020? I honestly doubt we'll see the SLS launch before 2024 at it's current rate.
In 2017 the SLS launch was about 2 years out, but likely to slip: https://www.nasaspaceflight.com/2017/11/sls-managers-troops-...
In 2019 the SLS launch is a bit under 2 years out, but likely to slip: https://arstechnica.com/science/2019/02/nasa-still-working-t...
This strongly reminds me of the fact that late software projects are promised to be on time until about 6 weeks before launch, and then launch keeps getting delayed. And this is true no matter how late it eventually turns out to be. The reason why 6 weeks is the magic figure is that for a software project, that's the point where you can no longer paper over the inevitability of failure with wishful thinking. Rockets have slower schedule, but it is strongly looking like 2 years is a similar magic figure in that industry, for similar reasons.
In that light, the money quote from the second article is this:
However, the agency and its prime contractor for the core stage, Boeing, are on a tight timeline that has little margin for technical problems that might occur during the structural tests of the tank or the green run tests. Historically, during this integration and test process with other large rocket programs, major problems have often occurred.
I am generally a believer that what happened historically shouldn't be ignored. There is therefore no way that the SLS will launch in 2020. Or 2021. In fact nobody really knows when it will launch. Furthermore the upper stage, aka Orion, is apparently in even worse shape. Right now they are going back to the drawing board to try to find a design that gets costs down.
Admittedly SpaceX itself is promising the BFR in about 2 years, and also had a history of overruns. I don't think that they will launch on time. But they have a better history of getting launch vehicles up.
I will therefore happily take your bet for $100, but I would like to formalize it a bit. I win if Falcon Super Heavy+Starship or whatever it gets renamed to gets successfully launched to orbit first OR if SLS+Orion gets canceled first. Vice versa you win if SLS+Orion gets successfully launched first OR if Falcon Super Heavy+Starship or whatever gets canceled first. Note that "SpaceX goes out of business" counts as canceled, even if someone else (eg Bezos) buys the remnants and then launches something based on the work.
If my version is acceptable, you can contact me by email per my profile.
That said, I'm still on the side of betting with history. In most organizations, the deadline is the first date that nobody can (yet) disprove. When a deadline depends on problems not happening on this project that historically have been common, I think it is safe to bet that history will repeat itself.
This goes doubly for the SLS. Which is more ambitious than past launch systems, and is being built so long after the last new launch system was designed by the companies involved that there is little institutional knowledge left about how to do it. (Furthermore building with competing companies contracting for pieces that need to integrate just sounds like a recipe for expensive overruns to me.)
As opposed to the BFR. Which is being designed by a company with more recent experience of how to build new launch systems than the rest of the planet put together.
The Starship hopper will definitely be working long before either of those two take flight.