Both are awesome tools, but for variables, I always Data Jar. Unfortunately, at the moment, Data Jar is broken in i*OS 14 (public beta). @simonbs has created a workaround in a TestFlight beta, but that is also having issues. Here is a Tweet from datajarapp a couple of days ago.
I really hope it gets fixed by Apple as it is such a useful app and I have a lot of Shortcuts that use it.