I have just recently migrated, but to be honest, I ended up using both. I prefer Obsidian general speaking, but there are some things I MUCH prefer in Roam (WYSIWYG, block/outliner format, no friction input). If you don’t want to be caught between features that you like in one app but isn’t available in the other (there are plenty of things in Obsidian that I like better such as the graph, the community (!), the plugins that don’t slow down the app, the speed generally!), I’d say decide on one app and do the course for that app.
Also, you’ll want to do some clean-up or be aware of some ways NOT to name your files in Roam (e.g. [[Books/the special book]]
Also, look here for some of my experience…
Good luck!